Gimp: heap out-of-bounds reads in iff/ilbm loader from ham row size mismatch and nplanes=0

A flaw was found in the file-iff (IFF/ILBM) plugin in GIMP. When processing a specially crafted IFF/ILBM image file, the plugin does not properly validate the HAM row size and improperly handles cases where the number of color planes (nPlanes) is zero. This causes a row size mismatch that bypasses memory bounds checking, resulting in heap out-of-bounds reads. This issue can result in an application crash, leading to a denial of service or a limited information disclosure of heap memory contents.