fix: Add missing mounted check to mxcImage

lib/widgets/mxc_image.dart

@@ -66,6 +66,7 @@ class _MxcImageState extends State<MxcImage> {
   }
 
   Future<void> _load() async {
+    if (!mounted) return;
     final client =
         widget.client ?? widget.event?.room.client ?? Matrix.of(context).client;
     final uri = widget.uri;