AnimEncoder: avoid freeing uninitialized memory pointer.
AnimEncoder: avoid freeing uninitialized memory pointer.

In GenerateCandidates(), when candidate_ll->evaluate_ and
candidate_lossy->evaluate_ are both true, if lossless encoding
exits on error, candidate_ll->evaluate_ would not be correctly
reset. This will cause freeing uninitialized memory pointer in
SetFrame().

BUG=webp:322

Change-Id: I481b49a186e4fa3607ce71b4543a481083edf444

webmproject/libwebp,webmproject/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp,PKRoma/libwebp,PKRoma/libwebp,PKRoma/libwebp,webmproject/libwebp