7.1.2

Fix another regression seeking PNG files

This fixes a regression introduced in 7.1.0 when adding support for APNG files.

When calling seek(n) on a regular PNG where n > 0, it failed to raise an EOFError as it should have done, resulting in:

AttributeError: 'NoneType' object has no attribute 'read'

Pillow 7.1.2 now raises the correct exception.