feat: filter the empty delta

frontend/app_flowy/packages/flowy_editor/lib/src/document/text_delta.dart

@@ -417,7 +417,8 @@ class Delta extends Iterable<TextOperation> {
 
           // Optimization if rest of other is just retain
           if (!otherIter.hasNext &&
-              delta._operations[delta._operations.length - 1] == newOp) {
+              delta._operations.isNotEmpty &&
+              delta._operations.last == newOp) {
             final rest = Delta(thisIter.rest());
             return (delta + rest)..chop();
           }

frontend/app_flowy/packages/flowy_editor/lib/src/operation/transaction_builder.dart

@@ -203,6 +203,9 @@ class TransactionBuilder {
     for (var i = 0; i < operations.length; i++) {
       op = transformOperation(operations[i], op);
     }
+    if (op is TextEditOperation && op.delta.isEmpty) {
+      return;
+    }
     operations.add(op);
   }
 

frontend/app_flowy/packages/flowy_editor/lib/src/service/internal_key_event_handlers/enter_without_shift_in_text_node_handler.dart

@@ -86,7 +86,7 @@ FlowyKeyEventHandler enterWithoutShiftInTextNodesHandler =
       );
       TransactionBuilder(editorState)
         ..insertNode(
-          textNode.path,
+          textNode.path.next,
           TextNode.empty(),
         )
         ..afterSelection = afterSelection