rtmpproto: Make sure to pass on the error code if read_connect failed

Previously, if read_connect failed, the ret variable was unmodified
and had the value 0, indicating success, which then was returned from
the rtmp_open function, even though it actually failed.

CC: libav-stable@libav.org
Signed-off-by: Martin Storsjö <martin@martin.st>
(cherry picked from commit 6477139721)

libavformat/rtmpproto.c

@@ -2443,7 +2443,7 @@ reconnect:
         if ((ret = gen_connect(s, rt)) < 0)
             goto fail;
     } else {
-        if (read_connect(s, s->priv_data) < 0)
+        if ((ret = read_connect(s, s->priv_data)) < 0)
             goto fail;
         rt->is_input = 1;
     }