avcodec/h264: do not leave ret random on minor failures, causing major failure

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

libavcodec/h264.c

@@ -1751,6 +1751,7 @@ again:
             goto end;
     }
 
+    ret = 0;
 end:
     /* clean up */
     if (h->cur_pic_ptr && !h->droppable) {