Do not attempt to read IFD1 if absent

[radarhere]

#6748 added reading of IFD1 in Image.Exif.

However, I didn't consider that zero is a special value for the offset to the next IFD.

https://www.media.mit.edu/pia/Research/deepview/exif.html

If its value is '0x00000000', it means this is the last IFD and there is no linked IFD.

So if that is the case, don't attempt to read IFD1.

This fixes some warnings that are shown at the moment - https://github.com/python-pillow/Pillow/actions/runs/3799772426/jobs/6462615701#step:8:4148

Tests/test_file_tiff.py::TestFileTiff::test_get_child_images[Tests/images/hopper.tif-sizes0]
Tests/test_file_tiff.py::TestFileTiff::test_get_child_images[Tests/images/child_ifd.tiff-sizes1]
Tests/test_file_tiff.py::TestFileTiff::test_get_child_images[Tests/images/child_ifd_jpeg.tiff-sizes2]
/opt/hostedtoolcache/Python/3.11.1/x64/lib/python3.11/site-packages/PIL/TiffImagePlugin.py:852: UserWarning: Truncated File Read
warnings.warn(str(msg))