avutil/buffer: Avoid moving the AVBufferRef to a new place in memory in av_buffer_realloc()

This allows reallocating AVBufferRefs without the need to update
all pointers to it
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/buffer.c

@@ -201,8 +201,7 @@ int av_buffer_realloc(AVBufferRef **pbuf, int size)
 
         memcpy(new->data, buf->data, FFMIN(size, buf->size));
 
-        av_buffer_unref(pbuf);
-        *pbuf = new;
+        buffer_replace(pbuf, &new);
         return 0;
     }