CLSA-2026-1773655369 gimp: Fix of 4 CVEs

CVE-2026-2044: fix uninitialized memory read in PGM file parser - CVE-2026-2045: fix heap buffer overflow in XWD file loader - CVE-2026-2048: fix out-of-bounds write in XWD file loader - CVE-2026-0797: fix missing fread return value checks in ICO file loader...

The PPM reader in libjpeg-turbo through 2.0.90 mishandles use of tjLoadImage for loading a 16-bit binary PPM file into a grayscale buffer and loading a 16-bit binary PGM file into an RGB buffer. This is related to a heap-based buffer overflow in the get_word_rgb_row function in rdppm.c.

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