Sensible defaults

In the wmaker-dev list, Iain noted that:

  "I can see the benefit of this.  I know of at least two
   applications[1] which don't bother to set a class and instance.  Early
   versions of my OS X cycling patch for Window Maker caused a crash when
   faced with such windows because I forgot to check that these
   properties existed.  Nowadays it just refuses to do the cycling.

   Also Window Maker won't let you save attributes on such windows from
   the Inspector.

   [1] Interestingly they are competiting commercial applications: No
   Machine and Exceed onDemand."

[crmafra: edit commit log]

src/properties.c

@@ -72,8 +72,8 @@ int PropGetWMClass(Window window, char **wm_class, char **wm_instance)
 
 	class_hint = XAllocClassHint();
 	if (XGetClassHint(dpy, window, class_hint) == 0) {
-		*wm_class = NULL;
-		*wm_instance = NULL;
+		*wm_class = strdup("default");
+		*wm_instance = strdup("default");
 		XFree(class_hint);
 		return False;
 	}