Rework internals of ApiRequestPager (#518)

## Description
Changes how `init()` works for `ApiRequestPager` so that it 1) always
forces updating the total count if needed and 2) propagates errors
during the initial fetch up to the original caller

This means if an error occurs during the initialization of the pager
data, it won't be quietly logged and ignored. Instead, ViewModel code
will catch it and display an error in the UI.

### Related issues
Should fix #492

app/src/main/java/com/github/damontecres/wholphin/ui/components/CollectionFolderGrid.kt

@@ -252,13 +252,26 @@ class CollectionFolderViewModel
                     this@CollectionFolderViewModel.sortAndDirection.value = sortAndDirection
                     this@CollectionFolderViewModel.filter.value = filter
                 }
-                val newPager = createPager(sortAndDirection, recursive, filter, useSeriesForPrimary)
-                newPager.init()
-                if (newPager.isNotEmpty()) newPager.getBlocking(0)
-                withContext(Dispatchers.Main) {
-                    pager.value = newPager
-                    loading.value = LoadingState.Success
-                    backgroundLoading.value = LoadingState.Success
+                try {
+                    val newPager =
+                        createPager(sortAndDirection, recursive, filter, useSeriesForPrimary).init()
+                    if (newPager.isNotEmpty()) newPager.getBlocking(0)
+                    withContext(Dispatchers.Main) {
+                        pager.value = newPager
+                        loading.value = LoadingState.Success
+                        backgroundLoading.value = LoadingState.Success
+                    }
+                } catch (ex: Exception) {
+                    Timber.e(
+                        ex,
+                        "Exception while loading data: sort=%s, filter=%s",
+                        sortAndDirection,
+                        filter,
+                    )
+                    withContext(Dispatchers.Main) {
+                        loading.value = LoadingState.Error(ex)
+                        pager.value = listOf()
+                    }
                 }
             }
         }

app/src/main/java/com/github/damontecres/wholphin/util/ApiRequestPager.kt

@@ -66,7 +66,7 @@ class ApiRequestPager<T>(
 
     suspend fun init(initialPosition: Int = 0): ApiRequestPager<T> {
         if (totalCount < 0) {
-            fetchPage(initialPosition, true).join()
+            fetchPageBlocking(initialPosition, true)
         }
         return this
     }
@@ -75,7 +75,7 @@ class ApiRequestPager<T>(
         if (index in 0..<totalCount) {
             val item = items[index]
             if (item == null) {
-                fetchPage(index, false)
+                fetchPage(index)
             }
             return item
         } else {
@@ -87,7 +87,7 @@ class ApiRequestPager<T>(
         if (index in 0..<totalCount) {
             val item = items[index]
             if (item == null) {
-                fetchPage(index, false).join()
+                fetchPageBlocking(index, false)
                 return items[index]
             }
             return item
@@ -110,33 +110,37 @@ class ApiRequestPager<T>(
     override val size: Int
         get() = totalCount
 
-    private fun fetchPage(
+    private fun fetchPage(position: Int): Job =
+        scope.launch(ExceptionHandler() + Dispatchers.IO) {
+            fetchPageBlocking(position, false)
+        }
+
+    private suspend fun fetchPageBlocking(
         position: Int,
         setTotalCount: Boolean,
-    ): Job =
-        scope.launch(ExceptionHandler() + Dispatchers.IO) {
-            mutex.withLock {
-                val pageNumber = position / pageSize
-                if (cachedPages.getIfPresent(pageNumber) == null) {
-                    if (DEBUG) Timber.v("fetchPage: $pageNumber")
-                    val newRequest =
-                        requestHandler.prepare(
-                            request,
-                            pageNumber * pageSize,
-                            pageSize,
-                            setTotalCount,
-                        )
-                    val result = requestHandler.execute(api, newRequest).content
-                    if (setTotalCount) {
-                        totalCount = result.totalRecordCount
-                    }
-                    val data = mutableListOf<BaseItem>()
-                    result.items.forEach { data.add(BaseItem.from(it, api, useSeriesForPrimary)) }
-                    cachedPages.put(pageNumber, data)
-                    items = ItemList(totalCount, pageSize, cachedPages.asMap())
+    ) {
+        mutex.withLock {
+            val pageNumber = position / pageSize
+            if (cachedPages.getIfPresent(pageNumber) == null || setTotalCount) {
+                if (DEBUG) Timber.v("fetchPage: $pageNumber")
+                val newRequest =
+                    requestHandler.prepare(
+                        request,
+                        pageNumber * pageSize,
+                        pageSize,
+                        setTotalCount,
+                    )
+                val result = requestHandler.execute(api, newRequest).content
+                if (setTotalCount) {
+                    totalCount = result.totalRecordCount.coerceAtLeast(0)
                 }
+                val data = mutableListOf<BaseItem>()
+                result.items.forEach { data.add(BaseItem.from(it, api, useSeriesForPrimary)) }
+                cachedPages.put(pageNumber, data)
+                items = ItemList(totalCount, pageSize, cachedPages.asMap())
             }
         }
+    }
 
     suspend fun refreshItem(
         position: Int,