WPrefs: Marked args as unused for compiler in X Error handler

When an error occurs in X, the Xlib is using a callback mechanism to
execute application code to handle the problem, which means having a
fixed argument list for that application function.

It is then correct to not use all the arguments, so this patch adds the
appropriate stuff to avoid a false report from compiler.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>

WPrefs.app/editmenu.c

@@ -941,6 +941,10 @@ static void slideWindow(Display * dpy, Window win, int srcX, int srcY, int dstX,
 
 static int errorHandler(Display * d, XErrorEvent * ev)
 {
+	/* Parameter not used, but tell the compiler that it is ok */
+	(void) d;
+	(void) ev;
+
 	/* just ignore */
 	return 0;
 }