Remove padding between interleaved PCX palette data

[radarhere]

Resolves #8952

#535 added code to remove padding between bands.

Pillow/src/libImaging/PcxDecode.c

Lines 67 to 73 in 8e5a15b

	for (i = 1; i < bands; i++) { // note -- skipping first band
	memmove(
	&state->buffer[i * state->xsize],
	&state->buffer[i * stride],
	state->xsize
	);
	}

However, that didn't consider that there might be padding between lines for interleaved data, like the P;4L image from the issue.

I've created the test image using Pillow and manual hexediting.

[hugovk]

Thanks!