libtiff's tiffcrop utility has a uint32_t underflow that can lead to out of bounds read and write

libtiff's tiffcrop utility has a uint32_t underflow that can lead to out of bounds read and write. An attacker who supplies a crafted file to tiffcrop (likely via tricking a user to run tiffcrop on it with certain parameters) could cause a crash or in some cases, further exploitation.