update to v1.2.0-8-g20ceff7e

https://chromium.googlesource.com/webm/libwebp/+log/v1.2.0..v1.2.0-8-g20ceff7e

20ceff7e Fix OOB write in BuildHuffmanTable.
258f74e8 GetBackwardReferences: fail on alloc error
d21fa8d4 BackwardReferencesHashChainDistanceOnly: fix segfault on OOM
34ddf5b2 VP8LEncodeStream: fix segfault on OOM
17674ecf alpha_processing_neon.c: fix 0x01... typo
7dfde712 alpha_processing_neon.c: fix Dispatch/ExtractAlpha_NEON
059d4a59 Fix lossless encoding for MIPS.
113968ca pngdec: check version before using png_get_chunk_malloc_max

Bug: 299477569
Merged-In: I27c355c9970909fa5879e22e9f48b62acda386ef
Merged-In: I31c36dbf3aa78d35ecf38706b50464fd3d375741
Merged-In: Ic46c8cc324b1b2afe46f3a0d9d9b5205d92b2e18
Merged-In: Iaf8c74fe2b67925a577385be521791da42d47339
Change-Id: I627bc9605c25ff01db2c12d53833fb2c8cb74fc1
11 files changed