Init state to -1 in h264 parser.

Init state to -1 in h264 parser.
Fix:
==22063== Conditional jump or move depends on uninitialised value(s)
==22063==    at 0x811A4B7: ff_find_start_code (mpegvideo.c:99)
==22063==    by 0x82F5B74: parse_nal_units (h264_parser.c:132)
==22063==    by 0x82F5A68: h264_parse (h264_parser.c:261)
[...]
==22063==  Uninitialised value was created by a stack allocation
==22063==    at 0x82F5AF5: parse_nal_units (h264_parser.c:112)

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@18479 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b