Dismiss add manga snackbar when leaving controller (closes #3614)

app/src/main/java/eu/kanade/tachiyomi/ui/manga/MangaController.kt

@@ -130,14 +130,15 @@ class MangaController :
     private var chaptersHeaderAdapter: MangaChaptersHeaderAdapter? = null
     private var chaptersAdapter: ChaptersAdapter? = null
 
-    /**
-     * Sheet containing filter/sort/display items.
-     */
+    // Sheet containing filter/sort/display items.
     private var settingsSheet: ChaptersSettingsSheet? = null
 
     private var actionFab: ExtendedFloatingActionButton? = null
     private var actionFabScrollListener: RecyclerView.OnScrollListener? = null
 
+    // Snackbar to add manga to library after downloading chapter(s)
+    private var addSnackbar: Snackbar? = null
+
     /**
      * Action mode for multiple selection.
      */
@@ -316,6 +317,7 @@ class MangaController :
         chaptersHeaderAdapter = null
         chaptersAdapter = null
         settingsSheet = null
+        addSnackbar?.dismiss()
         updateToolbarTitleAlpha(255)
         super.onDestroyView(view)
     }
@@ -891,7 +893,7 @@ class MangaController :
         val manga = presenter.manga
         presenter.downloadChapters(chapters)
         if (view != null && !manga.favorite) {
-            activity!!.root_coordinator?.snack(view.context.getString(R.string.snack_add_to_library), Snackbar.LENGTH_INDEFINITE) {
+            addSnackbar = activity!!.root_coordinator?.snack(view.context.getString(R.string.snack_add_to_library), Snackbar.LENGTH_INDEFINITE) {
                 setAction(R.string.action_add) {
                     addToLibrary(manga)
                 }