RTSP/RTMP source: fix error 'no one is publishing to path' that happens after some seconds, when sourceOnDemand is enabled (#334)

internal/path/path.go

@@ -479,13 +479,13 @@ func (pa *Path) removeClient(c client.Client) {
 }
 
 func (pa *Path) onSourceSetReady() {
-	pa.sourceState = sourceStateReady
-
 	if pa.sourceState == sourceStateWaitingDescribe {
 		pa.describeTimer.Stop()
 		pa.describeTimer = newEmptyTimer()
 	}
 
+	pa.sourceState = sourceStateReady
+
 	for _, req := range pa.describeRequests {
 		req.Res <- client.DescribeRes{pa.sourceTracks.Write(), "", nil} //nolint:govet
 	}