sbbs_t::incom() should return NOINP immediately if/when socket disconnected

JS console.inkey() and friends use this as the underlying function to get
input from the TCP socket.

This might address issue #725

Hoping Nelgin will let us know.

src/sbbs3/main.cpp

@@ -2244,6 +2244,7 @@ void input_thread(void *arg)
 	}
 	sbbs->online=false;
 	sbbs->sys_status|=SS_ABORT;	/* as though Ctrl-C were hit */
+	SetEvent(sbbs->inbuf.data_event); // terminate incom() wait
 
     sbbs->input_thread_running = false;
 	sbbs->terminate_output_thread = true;
@@ -3961,6 +3962,9 @@ int sbbs_t::incom(unsigned int timeout)
 {
 	uchar	ch;
 
+	if(!online)
+		return NOINP;
+
 	// If we think we may have some input, send all our output
 	if (RingBufFull(&outbuf) != 0) {
 		SetEvent(outbuf.highwater_event);