context: add sanity-check to tile dimensions/resolution

[lovell]

The libvips' fuzz tests found a possible integer overflow here:

libheif/libheif/context.cc

Line 1938 in 7c9729e

y0 += tile_height;

/src/libheif/libheif/context.cc:1938:8: runtime error: signed integer overflow: 1344282656 + 1344282656 cannot be represented in type 'int'
0 0x5b6b1f26031b in HeifContext::decode_full_grid_image(unsigned int, std::__1::shared_ptr<HeifPixelImage>&, std::__1::vector<unsigned char, std::__1::allocator<unsigned char>> const&, heif_decoding_options const&) const libheif/libheif/context.cc:1938
1 0x5b6b1f258489 in HeifContext::decode_image_planar(unsigned int, std::__1::shared_ptr<HeifPixelImage>&, heif_colorspace, heif_decoding_options const&, bool) const libheif/libheif/context.cc:1512
2 0x5b6b1f256d36 in HeifContext::decode_image_user(unsigned int, std::__1::shared_ptr<HeifPixelImage>&, heif_colorspace, heif_chroma, heif_decoding_options const&) const libheif/libheif/context.cc:1324
3 0x5b6b1f15d2c2 in heif_decode_image [libheif/libheif/api/libheif/heif.cc:1083]

Adding a sanity check on the dimensions of each tile as it is processed seems to do the job of preventing this logic being reached, although there may be additional/alternative solutions too.

[farindk]

Thank you. I've added a few more tests.

[farindk]

This should also fix issue 70126 in oss-fuzz