libwebp: Fix of 6 CVEs

CVE-2018-25009: fix out-of-bounds read in GetLE16 by validating VP8X chunk size - CVE-2018-25010: fix heap-based buffer overflow in ApplyFilter by limiting filter radius to image dimensions - CVE-2018-25011: fix heap-based buffer overflow in PutLE16 by rejecting multiple image chunks in ANMF...