Center the title of dialog boxes.

================================================================================
--- mc-4.6.1-pre2b/src/dialog.c
+++ mc-4.6.1-pre2b/src/dialog.c
@@ -162,7 +162,7 @@
 
     if (h->title) {
 	attrset (HOT_NORMALC);
-	dlg_move (h, space, (h->cols - strlen (h->title)) / 2);
+	dlg_move (h, space, (h->cols - mbstrlen (h->title)) / 2);
 	addstr (h->title);
     }
 }