[dev] dmenu segfaults when pressing control+enter without a selection

[Matthew of Boswell]

Hello,

I found this bug while accidentally pressing control+enter when I did a
quick control+y+enter for opening pages in surf. After doing this
dozens of times per day, I tracked down what was causing it.

Fix attached.

-- 
Matt Boswell
--- dmenu_old.c	2015-10-15 17:49:27.521943292 -0400
+++ dmenu.c	2015-10-15 17:49:20.355108883 -0400
@@ -370,7 +370,7 @@
 		puts((sel && !(ev->state & ShiftMask)) ? sel->text : text);
 		if(!(ev->state & ControlMask))
 			exit(EXIT_SUCCESS);
-		sel->out = True;
+		if (sel) sel->out = True;
 		break;
 	case XK_Right:
 		if(text[cursor] != '\0') {