Fixed comparison warning

[radarhere]

https://github.com/python-pillow/Pillow/runs/1649086275#step:9:118

src/libImaging/TiffDecode.c:241:22: warning: comparison of integers of different signs: 'int' and 'uint32' (aka 'unsigned int') [-Wsign-compare]
if (state->xsize != img.width || state->ysize != img.height) {
~~~~~~~~~~~~ ^ ~~~~~~~~~
src/libImaging/TiffDecode.c:241:51: warning: comparison of integers of different signs: 'int' and 'uint32' (aka 'unsigned int') [-Wsign-compare]
if (state->xsize != img.width || state->ysize != img.height) {
~~~~~~~~~~~~ ^ ~~~~~~~~~~
src/libImaging/TiffDecode.c:582:41: warning: comparison of integers of different signs: 'int' and 'unsigned int' [-Wsign-compare]
for (tile_y = 0; tile_y < current_tile_length; tile_y++) {
~~~~~~ ^ ~~~~~~~~~~~~~~~~~~~
3 warnings generated.

[wiredfool]

I'm not sure that this is the right approach for a couple of reasons.

1. We should probably not be using the U/INT32 for these in general, they should really be tsize_t or whatever they are in libtiff, because they change over time. Some of the libtiff items have definitely changed from u/int32 -> u/int64 over the time that I've been digging into valgrind.

2. If we're casting like that, we need to make sure that we're not going to under/overflow in the cast. Basically, it's silencing the warning, but it doesn't actually change the behavior.

[radarhere]

Thanks.
I've updated to remove the casting change, and kept the second change.

[radarhere]

This looks like it became part of #5364.