Fix libtiff cleanup

[radarhere]

Alternative to #8992

I've found that since #8954 was merged, there have been intermittent errors.

• 'cannot identify image file' - https://github.com/python-pillow/Pillow/actions/runs/15371601710/job/43251458128
• 'attempt to seek outside sequence' - https://github.com/python-pillow/Pillow/actions/runs/15370070907/job/43247953625
• 'unrecognized data stream contents when reading image file' - https://github.com/python-pillow/Pillow/actions/runs/15370070907/job/43247953635

Testing, I find that the minimal change to fix the problem is to restore one of the calls to TIFFCleanup, and then to set clientstate->tiff = NULL to prevent ImagingLibTiffEncodeCleanup from running afterwards.