libavcodec/webp: treat out-of-bound palette index as translucent black

See https://code.google.com/p/webp/issues/detail?id=206
for a description of the problem/fix.

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

This patch makes the decoder follow the recommendation of the spec.
There is some disagreement (see "[FFmpeg-devel] [PATCH]: libavcodec/webp")
about what would be best to be written in the spec, so in case the spec
is changed again, this potentially would need to be amended or reverted
(cherry picked from commit 4fd21d58a72c38ab63c3a4483b420db260fa7b8d)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
avcodec/libilbc: support for latest git of libilbc

in the latest git commits of libilbc developers removed WebRtc_xxx typedefs

This commit uses int types instead,
it's safe to apply also for previous versions since
WebRtc_Word16 was always a typedef of int16_t and
WebRtc_UWord16 a typedef of uint16_t

Reviewed-by: Timothy Gu <timothygu99@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 59af5383c18c8cf3fe2a4b5cc1ebf2f3300bdfe5)

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>