Display "(Queue is empty)" if queue is empty.

scripts/tkremind

@@ -2703,9 +2703,14 @@ proc ShowQueue { file } {
 	    continue;
 	}
         set obj [lsort -command sort_q $obj]
+        set did 0
 	foreach q $obj {
 	    $w.t insert end "$q\n"
+            set did 1
 	}
+        if { $did == 0 } {
+            $w.t insert end "(Queue is empty)\n"
+        }
     }
     $w.t configure -state disabled
 }