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

@@ -57,18 +57,23 @@ class QuillController extends ChangeNotifier {
       if (delta == null) {
         _updateSelection(textSelection, ChangeSource.LOCAL);
       } else {
-        Delta user = Delta()
-          ..retain(index)
-          ..insert(data)
-          ..delete(len);
-        int positionDelta = getPositionDelta(user, delta);
-        _updateSelection(
-          textSelection.copyWith(
-            baseOffset: textSelection.baseOffset + positionDelta,
-            extentOffset: textSelection.extentOffset + positionDelta,
-          ),
-          ChangeSource.LOCAL,
-        );
+        try {
+          Delta user = Delta()
+            ..retain(index)
+            ..insert(data)
+            ..delete(len);
+          int positionDelta = getPositionDelta(user, delta);
+          _updateSelection(
+            textSelection.copyWith(
+              baseOffset: textSelection.baseOffset + positionDelta,
+              extentOffset: textSelection.extentOffset + positionDelta,
+            ),
+            ChangeSource.LOCAL,
+          );
+        } catch (e) {
+          print ('getPositionDelta or getPositionDelta error: $e');
+          throw e;
+        }
       }
     }
     notifyListeners();