Show toast if we save to fail file to gallery

lib/generated/intl/messages_en.dart

@@ -618,6 +618,8 @@ class MessageLookup extends MessageLookupByLibrary {
         "faqs": MessageLookupByLibrary.simpleMessage("FAQs"),
         "favorite": MessageLookupByLibrary.simpleMessage("Favorite"),
         "feedback": MessageLookupByLibrary.simpleMessage("Feedback"),
+        "fileFailedToSaveToGallery": MessageLookupByLibrary.simpleMessage(
+            "Failed to save file to gallery"),
         "fileInfoAddDescHint":
             MessageLookupByLibrary.simpleMessage("Add a description..."),
         "fileSavedToGallery":

lib/generated/l10n.dart

@@ -5663,6 +5663,16 @@ class S {
     );
   }
 
+  /// `Failed to save file to gallery`
+  String get fileFailedToSaveToGallery {
+    return Intl.message(
+      'Failed to save file to gallery',
+      name: 'fileFailedToSaveToGallery',
+      desc: '',
+      args: [],
+    );
+  }
+
   /// `Download`
   String get download {
     return Intl.message(

lib/l10n/intl_en.arb

@@ -791,6 +791,7 @@
   "close": "Close",
   "setAs": "Set as",
   "fileSavedToGallery": "File saved to gallery",
+  "fileFailedToSaveToGallery": "Failed to save file to gallery",
   "download": "Download",
   "pressAndHoldToPlayVideo": "Press and hold to play video",
   "downloadFailed": "Download failed",

lib/ui/tools/collage/collage_save_button.dart

@@ -49,7 +49,11 @@ class SaveCollageButton extends StatelessWidget {
               compressedBytes,
               title: fileName,
             ));
-            final newFile = await File.fromAsset("ente Collages", newAsset!);
+            if (newAsset == null) {
+              showShortToast(context, S.of(context).fileFailedToSaveToGallery);
+              return;
+            }
+            final newFile = await File.fromAsset("ente Collages", newAsset);
             SyncService.instance.sync();
             showShortToast(context, S.of(context).collageSaved);
             replacePage(