Use code for unknown error when initializing.

Any case where we hit the cleanup without otherwise setting err_code is some sort of caught error that we're not considering. May not be possible anymore

PIL/ImageFile.py

@@ -178,7 +178,7 @@ class ImageFile(Image.Image):
                     self.map = None
 
         self.load_prepare()
-        err_code = 0
+        err_code = -3 # initialize to unknown error
         if not self.map:
             # sort tiles in file order
             self.tile.sort(key=_tilesort)