avcodec/mpegvideo: Check pointer when allocation fail

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

libavcodec/mpegvideo.c

@@ -1045,11 +1045,14 @@ do {\
 
     if (s1->bitstream_buffer) {
         if (s1->bitstream_buffer_size +
-            FF_INPUT_BUFFER_PADDING_SIZE > s->allocated_bitstream_buffer_size)
+            FF_INPUT_BUFFER_PADDING_SIZE > s->allocated_bitstream_buffer_size) {
             av_fast_malloc(&s->bitstream_buffer,
                            &s->allocated_bitstream_buffer_size,
                            s1->allocated_bitstream_buffer_size);
-            s->bitstream_buffer_size = s1->bitstream_buffer_size;
+            if (!s->bitstream_buffer)
+                return AVERROR(ENOMEM);
+        }
+        s->bitstream_buffer_size = s1->bitstream_buffer_size;
         memcpy(s->bitstream_buffer, s1->bitstream_buffer,
                s1->bitstream_buffer_size);
         memset(s->bitstream_buffer + s->bitstream_buffer_size, 0,