display error if mount location is not found

web/repertory/lib/models/mount.dart

@@ -84,7 +84,7 @@ class Mount with ChangeNotifier {
         ),
       );
 
-      if (response.statusCode == 500) {
+      if (!unmount && response.statusCode == 500) {
         return false;
       }
 

web/repertory/lib/widgets/mount_widget.dart

@@ -163,7 +163,7 @@ class _MountWidgetState extends State<MountWidget> {
                                 _enabled = true;
                               });
 
-                              if (isActive || !context.mounted) {
+                              if (success || isActive || !context.mounted) {
                                 return;
                               }