put_bits: fix invalid shift by 32 in flush_put_bits()

If flush_put_bits() is called when the 32-bit buffer is empty,
e.g. after writing a multiple of 32 bits, and invalid shift by
32 is performed.  Since flush_put_bits() is called infrequently,
this additional check should have negligible performance impact.
Signed-off-by: Mans Rullgard <mans@mansr.com>

libavcodec/put_bits.h

@@ -78,7 +78,8 @@ static inline int put_bits_count(PutBitContext *s)
 static inline void flush_put_bits(PutBitContext *s)
 {
 #ifndef BITSTREAM_WRITER_LE
-    s->bit_buf<<= s->bit_left;
+    if (s->bit_left < 32)
+        s->bit_buf<<= s->bit_left;
 #endif
     while (s->bit_left < 32) {
         /* XXX: should test end of buffer */