libde265: SAO sequential filter heap buffer overflow via signed integer overflow

libde265 is an open source implementation of the h.265 video codec. Versions prior to 1.1.1 use signed 32-bit arithmetic to calculate the sample adaptive offset input-buffer size, allowing a crafted HEVC stream with large dimensions and 16-bit luma samples to cause an integer overflow, an undersized allocation, and an out-of-bounds heap read that may expose heap data in decoded output or crash the decoder. Version 1.1.1 contains a patch.