Call prot->url_close only if it is present.

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@11044 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

libavformat/avio.c

@@ -132,10 +132,11 @@ offset_t url_seek(URLContext *h, offset_t pos, int whence)
 
 int url_close(URLContext *h)
 {
-    int ret;
+    int ret = 0;
     if (!h) return 0; /* can happen when url_open fails */
 
-    ret = h->prot->url_close(h);
+    if (h->prot->url_close)
+        ret = h->prot->url_close(h);
     av_free(h);
     return ret;
 }