removed warnings

Originally committed as revision 2248 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/utils.c

@@ -222,6 +222,7 @@ void avcodec_default_release_buffer(AVCodecContext *s, AVFrame *pic){
     assert(pic->type==FF_BUFFER_TYPE_INTERNAL);
     assert(s->internal_buffer_count);
 
+    buf = NULL; /* avoids warning */
     for(i=0; i<s->internal_buffer_count; i++){ //just 3-5 checks so is not worth to optimize
         buf= &((InternalBuffer*)s->internal_buffer)[i];
         if(buf->data[0] == pic->data[0])