lavf/mux: Always call write_trailer() from av_write_trailer() to avoid a leak.

Fixes ticket #4049.

libavformat/mux.c

@@ -926,7 +926,7 @@ int av_write_trailer(AVFormatContext *s)
     for (;; ) {
         AVPacket pkt;
         ret = interleave_packet(s, &pkt, NULL, 1);
-        if (ret < 0) //FIXME cleanup needed for ret<0 ?
+        if (ret < 0)
             goto fail;
         if (!ret)
             break;
@@ -943,10 +943,14 @@ int av_write_trailer(AVFormatContext *s)
             goto fail;
     }
 
+fail:
     if (s->oformat->write_trailer)
+        if (ret >= 0) {
         ret = s->oformat->write_trailer(s);
+        } else {
+            s->oformat->write_trailer(s);
+        }
 
-fail:
     if (s->pb)
        avio_flush(s->pb);
     if (ret == 0)