fixed PY-8398 Change Signature: disable refactor and preview buttons in case of validation error in the dialog

python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureDialog.java

@@ -194,6 +194,12 @@ public class PyChangeSignatureDialog extends ChangeSignatureDialogBase<PyParamet
   @Override
   protected ValidationInfo doValidate() {
     final String message = validateAndCommitData();
+    SwingUtilities.invokeLater(new Runnable() {
+      public void run() {
+        getRefactorAction().setEnabled(message == null);
+        getPreviewAction().setEnabled(message == null);
+      }
+    });
     if (message != null) return new ValidationInfo(message);
     return super.doValidate();
   }