SplashOutputDev: Fix integer overflow in tilingPatternFill

SplashOutputDev: Fix integer overflow in tilingPatternFill

Origin: https://gitlab.freedesktop.org/poppler/poppler/-/commit/8352264766652b98336e92359a70b3161a9ab97a
Bug-Debian: https://bugs.debian.org/1138708
Bug: https://gitlab.freedesktop.org/poppler/poppler/-/work_items/1715
Bug-Debian-Security: https://security-tracker.debian.org/tracker/CVE-2026-10118

Use checkedMultiply() to check integer multiplication of surface size
and number of repetitions to avoid integer overflow and possible memory issues.

Fixes: #1715
Gbp-Pq: Name SplashOutputDev-Fix-integer-overflow-in-tilingPatter.patch