OSV-2024-1464 Use-of-uninitialized-value in Splash::compositeBackground

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=513891492 Crash type: Use-of-uninitialized-value Crash state: Splash::compositeBackground SplashOutputDev::setSoftMask Gfx::doSoftMask...