Do not assign new fp attribute to image when closing

[radarhere]

Suggestions for python-pillow#7557

• hasattr(self, "fp") shouldn't raise an exception, so I've moved it out of the try block. This also has the effect of not assigning fp = None on images that didn't have an fp before.
• Testing, I found that your logging test didn't fail when I removed the source code change. I've instead mirrored https://github.com/python-pillow/Pillow/blob/28c173f8d4767c7f6dd22dc840117fe641f4d3ee/Tests/test_image_load.py#L27-L32, and that does detect debug messages correctly.

[RaphaelVRossi]

Nice catch @radarhere! Thanks!