Fix low-res PNG problem by always loading high res of PNG files only

lib/controls/media_attachment_viewer_control.dart

@@ -43,7 +43,7 @@ class _MediaAttachmentViewerControlState
 
     if (item.explicitType == AttachmentMediaType.video) {
       return AVControl(
-        videoUrl: item.uri.toString(),
+        videoUrl: item.mainUri.toString(),
         width: width,
         height: height,
         description: item.description,
@@ -51,13 +51,13 @@ class _MediaAttachmentViewerControlState
       );
     }
     if (item.explicitType != AttachmentMediaType.image) {
-      return Text('${item.explicitType}: ${item.uri}');
+      return Text('${item.explicitType}: ${item.mainUri}');
     }
 
     return ImageControl(
       width: width,
       height: height,
-      imageUrl: item.thumbnailUri.toString(),
+      imageUrl: item.usableThumbnailUri.toString(),
       altText: item.description,
       onTap: openMediaScreenCallback,
     );

lib/models/media_attachment.dart

@@ -29,6 +29,12 @@ class MediaAttachment {
 
   final Visibility visibility;
 
+  late final String _extension;
+
+  Uri get mainUri => _extension == '.png' ? fullFileUri : uri;
+
+  Uri get usableThumbnailUri => _extension == '.png' ? fullFileUri : uri;
+
   MediaAttachment({
     required this.id,
     required this.uri,
@@ -40,7 +46,9 @@ class MediaAttachment {
     required this.explicitType,
     required this.description,
     required this.visibility,
-  });
+  }) {
+    _extension = p.extension(fullFileUri.path);
+  }
 
   MediaAttachment.randomBuilt()
       : id = randomId(),

lib/screens/media_viewer_screen.dart

@@ -107,7 +107,7 @@ class _MediaViewerScreenState extends State<MediaViewerScreen> {
           maxScale: 10.0,
           scaleFactor: 400,
           child: LoginAwareCachedNetworkImage(
-              imageUrl: currentAttachment.uri.toString()),
+              imageUrl: currentAttachment.mainUri.toString()),
         );
         break;
       case AttachmentMediaType.unknown: