self.filename might be undefined, use getattr

Still check `is None` as it might still be something false-ish, i guess.

IPython/core/display.py

@@ -655,7 +655,7 b' class JSON(DisplayObject):'
     @data.setter
     def data(self, data):
         if isinstance(data, str):
-            if self.filename is None:
+            if getattr(self, 'filename') is None:
                 warnings.warn("JSON expects JSONable dict or list, not JSON strings")
             data = json.loads(data)
         self._data = data
@@ -690,7 +690,7 b' class GeoJSON(JSON):'
     @data.setter
     def data(self, data):
         if isinstance(data, str):
-            if self.filename is None:
+            if getattr(self, 'filename') is None:
                 warnings.warn("GeoJSON expects JSONable dict or list, not JSON strings")
             data = json.loads(data)
         self._data = data