idoc/examples/remuxing: Use avio_closep() in examples as it avoids leaving stale pointers

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

doc/examples/remuxing.c

@@ -153,7 +153,7 @@ end:
 
     /* close output */
     if (ofmt_ctx && !(ofmt->flags & AVFMT_NOFILE))
-        avio_close(ofmt_ctx->pb);
+        avio_closep(&ofmt_ctx->pb);
     avformat_free_context(ofmt_ctx);
 
     if (ret < 0 && ret != AVERROR_EOF) {