CLSA-2026-1778861508 gimp: Fix of 2 CVEs

CVE-2026-4153: fix heap-based buffer overflow in PSP file parser by computing proper linewidth for bit depths 1 and 4 with small widths - CVE-2026-4154: fix integer overflow and buffer overflow in XPM file parser by adding GIMPMAXIMAGESIZE bounds checks and using gtrynew...