Fix getPositionDelta

lib/utils/diff_delta.dart

@@ -71,7 +71,7 @@ int getPositionDelta(Delta user, Delta actual) {
   DeltaIterator actualItr = DeltaIterator(actual);
   int diff = 0;
   while (userItr.hasNext || actualItr.hasNext) {
-    int length = math.min(userItr.peekLength(), actualItr.peekLength());
+    final length = math.min(userItr.peekLength(), actualItr.peekLength());
     Operation userOperation = userItr.next(length);
     Operation actualOperation = actualItr.next(length);
     if (userOperation.length != actualOperation.length) {

lib/widgets/controller.dart

@@ -57,6 +57,7 @@ class QuillController extends ChangeNotifier {
       if (delta == null) {
         _updateSelection(textSelection, ChangeSource.LOCAL);
       } else {
+        try {
           Delta user = Delta()
             ..retain(index)
             ..insert(data)
@@ -69,6 +70,10 @@ class QuillController extends ChangeNotifier {
             ),
             ChangeSource.LOCAL,
           );
+        } catch (e) {
+          print ('getPositionDelta or getPositionDelta error: $e');
+          throw e;
+        }
       }
     }
     notifyListeners();