cwm: avoid displaying empty menu

[Martin Brandenburg]

This avoids an empty square in the upper left corner if
there is nothing to display in some menu the user
requests.

-- Martin

Index: menu.c
===================================================================
RCS file: /cvs/xenocara/app/cwm/menu.c,v
retrieving revision 1.89
diff -u -p -r1.89 menu.c
--- menu.c      11 Nov 2015 14:22:01 -0000      1.89
+++ menu.c      20 Feb 2016 17:26:17 -0000
@@ -89,6 +89,9 @@ menu_filter(struct screen_ctx *sc, struc
        int                      evmask, focusrevert;
        int                      xsave, ysave, xcur, ycur;
 
+       if (TAILQ_EMPTY(menuq))
+               return NULL;
+
        TAILQ_INIT(&resultq);
 
        (void)memset(&mc, 0, sizeof(mc));