Add check if error not in ignoredError list

It was possible to add an error code more than one time if we don't change caret position after adding ignored error for the first time

python/src/com/jetbrains/python/validation/Pep8ExternalAnnotator.java

@@ -411,7 +411,9 @@ public class Pep8ExternalAnnotator extends ExternalAnnotator<Pep8ExternalAnnotat
         @Override
         public void consume(ModifiableModel model) {
           PyPep8Inspection tool = (PyPep8Inspection)model.getUnwrappedTool(PyPep8Inspection.INSPECTION_SHORT_NAME, file);
-          tool.ignoredErrors.add(myCode);
+          if (!tool.ignoredErrors.contains(myCode)) {
+            tool.ignoredErrors.add(myCode);
+          }
         }
       });
     }