Temporarily adding input_file_path to SceneFileWrite config. Not sure…

… why this isn't there already, or if there are problems with setting a default, but it fixed a weird bug that had arisen

manimlib/scene/scene_file_writer.py

@@ -34,6 +34,7 @@ class SceneFileWriter(object):
         # Previous output_file_name
         # TODO, address this in extract_scene et. al.
         "file_name": None,
+        "input_file_path": "",  # ??
         "output_directory": None,
     }