OSV-2020-1260 Negative-size-param in heif::HeifPixelImage::fill_RGB_16bit

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=13563 Crash type: Negative-size-param Crash state: heif::HeifPixelImage::fillRGB16bit heif::HeifContext::decodeoverlayimage heif::HeifContext::decodeimage...