src/systemcmds/topic_listener/listener_main.cpp: Fix topic_listener b…

…locking on user input

This fixes an earlier commit
     commit 0b60318
     Author: Jukka Laitinen <[email protected]>
     Date:   Fri Apr 22 16:40:13 2022 +0400

         src/systemcmds/topic_listener: Change topic listener to poll only on uorb

Signed-off-by: Jukka Laitinen <[email protected]>

src/systemcmds/topic_listener/listener_main.cpp

@@ -113,6 +113,9 @@ void listener(const orb_id_t &id, unsigned num_msgs, int topic_instance,
 
 		int time = 0;
 
+		// Make stdin non-blocking
+		fcntl(0, F_SETFL, O_NONBLOCK);
+
 		while (msgs_received < num_msgs) {
 
 			char c = 0;