obs-outputs: Fix bug (RTMP only working once)

This was caused to do the new RTMP code that added support for multiple
streams; the stream index needs to be reset on RTMP_Close otherwise it
will keep using the wrong stream information.

plugins/obs-outputs/librtmp/rtmp.c

@@ -4252,6 +4252,7 @@ RTMP_Close(RTMP *r)
         r->Link.streams[idx].playpath.av_val = NULL;
     }
 
+    r->Link.curStreamIdx = 0;
     r->Link.nStreams = 0;
 #endif
 }