Fix crash when saving unloaded images

app/src/main/kotlin/com/hippo/ehviewer/gallery/EhPageLoader.kt

@@ -45,8 +45,8 @@ class EhPageLoader(private val mGalleryInfo: GalleryInfo, startPage: Int) :
         EhUtils.getSuitableTitle(mGalleryInfo)
     }
 
-    override fun getImageExtension(index: Int): String {
-        return mSpiderQueen.getExtension(index)!!
+    override fun getImageExtension(index: Int): String? {
+        return mSpiderQueen.getExtension(index)
     }
 
     override fun save(index: Int, file: UniFile): Boolean {

app/src/main/kotlin/com/hippo/ehviewer/gallery/PageLoader2.kt

@@ -60,16 +60,15 @@ abstract class PageLoader2(private val gid: Long, var startPage: Int) : PageLoad
 
     protected abstract val title: String
 
-    protected abstract fun getImageExtension(index: Int): String
+    protected abstract fun getImageExtension(index: Int): String?
 
-    fun getImageFilename(index: Int): String {
-        return FileUtils.sanitizeFilename("$title - ${index + 1}.${getImageExtension(index).lowercase()}")
+    fun getImageFilename(index: Int): String? = getImageExtension(index)?.let {
+        FileUtils.sanitizeFilename("$title - ${index + 1}.${it.lowercase()}")
     }
 
     abstract fun save(index: Int, file: UniFile): Boolean
 
-    fun saveToDir(index: Int, dir: UniFile): UniFile? {
-        val filename = getImageFilename(index)
-        return (dir / filename).takeIf { save(index, it) }
+    fun saveToDir(index: Int, dir: UniFile): UniFile? = getImageFilename(index)?.let { filename ->
+        (dir / filename).takeIf { save(index, it) }
     }
 }

app/src/main/kotlin/com/hippo/ehviewer/ui/reader/PageActions.kt

@@ -86,6 +86,10 @@ suspend fun save(page: ReaderPage) {
     val cannotSave = getString(R.string.error_cant_save_image)
     if (granted) {
         val filename = getImageFilename(page.index)
+        if (filename == null) {
+            showSnackbar(cannotSave)
+            return
+        }
         val extension = FileUtils.getExtensionFromFilename(filename)
         val mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension) ?: "image/jpeg"
         val values = ContentValues()
@@ -133,6 +137,10 @@ suspend fun save(page: ReaderPage) {
 context(SnackbarHostState, Context, PageLoader2)
 suspend fun saveTo(page: ReaderPage) {
     val filename = getImageFilename(page.index)
+    if (filename == null) {
+        showSnackbar(getString(R.string.error_cant_save_image))
+        return
+    }
     val extension = FileUtils.getExtensionFromFilename(filename)
     val mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension) ?: "image/jpeg"
     page.runSuspendCatching {

app/src/main/kotlin/eu/kanade/tachiyomi/ui/reader/ReaderActivity.kt

@@ -430,7 +430,7 @@ class ReaderActivity : EhActivity() {
         lifecycleScope.launchIO {
             val granted = isAtLeastQ || requestPermission(Manifest.permission.WRITE_EXTERNAL_STORAGE)
             if (granted) {
-                val filename = mGalleryProvider!!.getImageFilename(index)
+                val filename = mGalleryProvider!!.getImageFilename(index) ?: return@launchIO makeToast(R.string.error_cant_save_image)
                 val extension = FileUtils.getExtensionFromFilename(filename)
                 val mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension) ?: "image/jpeg"
 
@@ -477,7 +477,7 @@ class ReaderActivity : EhActivity() {
 
     fun saveImageTo(index: Int) {
         lifecycleScope.launchIO {
-            val filename = mGalleryProvider?.getImageFilename(index) ?: return@launchIO
+            val filename = mGalleryProvider?.getImageFilename(index) ?: return@launchIO makeToast(R.string.error_cant_save_image)
             val extension = FileUtils.getExtensionFromFilename(filename)
             val mimeType = MimeTypeMap.getSingleton().getMimeTypeFromExtension(extension) ?: "image/jpeg"
             runSuspendCatching {