Prevent division by zero

[radarhere]

Resolves #8405. Alternative to #8406

The issue is concerned that at

Pillow/src/libImaging/FliDecode.c

Line 227 in 731bcda

if (INT32_MAX / state->xsize < state->ysize) {

state->xsize might be zero, and so we might be dividing by zero.

However, in the context of our library as a whole, images that say one of their dimensions are zero will be stopped at

Pillow/src/PIL/ImageFile.py

Lines 154 to 156 in 731bcda

	if not self.mode or self.size[0] <= 0 or self.size[1] <= 0:
	msg = "not identified by this driver"
	raise SyntaxError(msg)

Even if you consider just the C decoding process, we have

Pillow/src/decode.c

Lines 189 to 192 in 731bcda

	if (state->xsize <= 0 || state->xsize + state->xoff > (int)im->xsize ||
	state->ysize <= 0 || state->ysize + state->yoff > (int)im->ysize) {
	PyErr_SetString(PyExc_ValueError, "tile cannot extend outside image");
	return NULL;

So this is not a scenario that should actually occur. However, in order to allay concerns from a casual observer, it might be worth updating the code. I don't consider changes to address this to be a 'fix', but rather a 'If all else fails' safety net.

#8406 suggests resolving the concern by raising an error from within FliDecode.c. My minor concern with that strategy is that we could make someone reading the code think that xsize might be zero there.

Instead, I'm going to suggest just removing the division operation altogether.

if (INT32_MAX < (long)state->xsize * state->ysize) {

[Yay295]

long is not necessarily 64 bits. https://learn.microsoft.com/en-us/cpp/build/common-visual-cpp-64-bit-migration-issues
You should use int64_t.