CImg Library: Integer overflow in PNM size check bypasses memory guard (_load_pnm)

CImg Library is a C++ library for image processing. Prior to commit 4ca26bc, there is an integer overflow vulnerability in the W*H*D size computation inside _load_pnm() that can bypass the memory allocation guard. A crafted PNM/PGM/PPM file with large dimension values causes the overflow to wrap around, allocating an undersized buffer and potentially triggering a heap buffer overflow. Any application using CImg to load untrusted image files is affected. This issue has been patched via commit 4ca26bc.