jp2ksave: prevent heap buffer overflow on non-RGB images

[dloebl]

Similar to #5020, there is an OOB read/write (heap buffer overflow) in the save_as_ycc path if the input image isn't RGB. The Bands == 3 check that is already present in vips__foreign_save_jp2k_compress has to be applied to the regular jp2ksave build as well:

libvips/libvips/foreign/jp2ksave.c

Line 1338 in 9bde113

save_as_ycc = save_as_ycc && region->im->Bands == 3;

Reproducer:

./build-asan/tools/vips black --bands 1 out.jp2"[subsample-mode=on]" 32 32

==74562==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61a000000ac7 at pc 0x00010523b4d8 bp 0x00016bd76980 sp 0x00016bd76978
READ of size 1 at 0x61a000000ac7 thread T11
    #0 0x00010523b4d4 in vips_foreign_save_jp2k_rgb_to_ycc+0xd48 (libvips.42.dylib:arm64+0x474d4)
    #1 0x00010523d6e0 in vips_foreign_save_jp2k_write_block+0x36c (libvips.42.dylib:arm64+0x496e0)
    #2 0x000105695e6c in wbuffer_write_thread+0x134 (libvips.42.dylib:arm64+0x4a1e6c)
    #3 0x00010565c294 in vips_threadset_work+0x168 (libvips.42.dylib:arm64+0x468294)
    #4 0x00010565b230 in vips_thread_run+0x50 (libvips.42.dylib:arm64+0x467230)
    #5 0x0001048b58dc in g_thread_proxy+0x50 (libglib-2.0.0.dylib:arm64+0x558dc)
    #6 0x000105e02418 in asan_thread_start(void*)+0x4c (libclang_rt.asan_osx_dynamic.dylib:arm64e+0x3a418)
    #7 0x00018d939c04 in _pthread_start+0x84 (libsystem_pthread.dylib:arm64e+0x6c04)
    #8 0x00018d934ba4 in thread_start+0x4 (libsystem_pthread.dylib:arm64e+0x1ba4)