Limit total size of image instead of width and height individually.

[fancycode]

This allows processing panorama images with could be more than 32k pixels wide but a lot less than 32k pixexls high (e.g. 40000 x 5000 pixels). This fits in the memory limit defined by the previous 32k x 32k pixels limit but would be rejected without this PR.

[farindk]

Thank you, that makes sense.
But now we get an integer overflow somewhere:

file_fuzzer: /src/libheif/fuzzing/file_fuzzer.cc:41: void TestDecodeImage(struct heif_context *, const struct heif_image_handle *, size_t): Assertion `height >= 0' failed.

[fancycode]

Thank you, that makes sense. But now we get an integer overflow somewhere:

file_fuzzer: /src/libheif/fuzzing/file_fuzzer.cc:41: void TestDecodeImage(struct heif_context *, const struct heif_image_handle *, size_t): Assertion `height >= 0' failed.

Fixed (and added fuzzing input to corpus). The size check is now implemented in a central location so it doesn't need to be modified in lots of places if it needs to be changed in the future.

Problem was caused by a fuzzing input that had width 0 and height 4294967103. This then overflowed the height which was cast to int in

libheif/libheif/context.cc

Line 610 in ddb541a

image->set_resolution(width, height);

[farindk]

Thank you