fixed crash when saving empty menu items in wprefs

WPrefs.app/Menu.c

@@ -1625,6 +1625,8 @@ processData(char *title, ItemData *data)
 
     switch (data->type) {
      case ExecInfo:
+	if (data->param.exec.command == NULL)
+	    return NULL;
 #if 1
 	if (strpbrk(data->param.exec.command, "&$*|><?`=;")) {
 	    s1 = "SHEXEC";
@@ -1754,6 +1756,9 @@ processSubmenu(WEditMenu *menu)
 	    pl = processData(s, WGetEditMenuItemData(item));
 	}
 
+	if (!pl)
+	    continue;
+
 	PLAppendArrayElement(pmenu, pl);
     }