7.1.1

Fix regression seeking PNG files

This fixes a regression introduced in 7.1.0 when adding support for APNG files when callingseek and tell:

  1. >>> from PIL import Image
  2. >>> with Image.open("Tests/images/hopper.png") as im:
  3. ...     im.seek(0)
  4. ...
  5. Traceback (most recent call last):
  6.   File "<stdin>", line 2, in <module>
  7.   File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/PIL/PngImagePlugin.py", line 739, in seek
  8.     if not self._seek_check(frame):
  9.   File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/PIL/ImageFile.py", line 306, in _seek_check
  10.     return self.tell() != frame
  11.   File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/site-packages/PIL/PngImagePlugin.py", line 827, in tell
  12.     return self.__frame
  13. AttributeError: 'PngImageFile' object has no attribute '_PngImageFile__frame'
  14. >>>