MT#57405 warning: ignoring return value of 'int pipe(int*)'

This fixes that:

     AmRtpReceiver.cpp: In member function 'virtual void AmRtpReceiverThread::run()':
     AmRtpReceiver.cpp:92:7: warning: ignoring return value of 'int pipe(int*)' declared with attribute 'warn_unused_result' [-Wunused-result]
        92 |   pipe(fake_fds);
           |   ~~~~^~~~~~~~~~

Change-Id: I7a9488ce07f59955e94efa1812fb74cb86e2387d

core/AmRtpReceiver.cpp

@@ -89,7 +89,10 @@ void AmRtpReceiverThread::run()
 {
   // fake event to prevent the event loop from exiting
   int fake_fds[2];
-  pipe(fake_fds);
+
+  if (pipe(fake_fds))
+    WARN("Cannot read from pipe\n");
+
   struct event* ev_default =
     event_new(ev_base,fake_fds[0],
 	      EV_READ|EV_PERSIST,