avcodec/put_bits: Assert that there is enough space left in skip_put_bytes()

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
(cherry picked from commit 8f5ffed1)
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/put_bits.h

@@ -230,6 +230,7 @@ static inline void skip_put_bytes(PutBitContext *s, int n)
 {
     av_assert2((put_bits_count(s) & 7) == 0);
     av_assert2(s->bit_left == 32);
+    av_assert0(n <= s->buf_end - s->buf_ptr);
     s->buf_ptr += n;
 }