An attemp to fix the text selection bug (#1643)

lib/src/models/documents/document.dart

@@ -219,7 +219,7 @@ class Document {
     if (res.node is Line) {
       return res;
     }
-    final block = res.node as Block;
+    final block = res.node as Block; // TODO: Can be nullable, handle this case
     return block.queryChild(res.offset, true);
   }
 

lib/src/widgets/quill/quill_controller.dart

@@ -251,8 +251,13 @@ class QuillController extends ChangeNotifier {
       // updateSelection(
       // TextSelection.collapsed(offset: document.length), ChangeSource.LOCAL);
       updateSelection(
-          TextSelection.collapsed(offset: selection.baseOffset + len),
-          ChangeSource.local);
+        (selection.baseOffset + len) > 0
+            ? TextSelection.collapsed(
+                offset: selection.baseOffset + len,
+              )
+            : TextSelection.collapsed(offset: document.length),
+        ChangeSource.local,
+      );
     } else {
       // no need to move cursor
       notifyListeners();