Fix use-after-free

menu_settings_iterate() would strcmp freed labels after exiting
a submenu.
Merge pull request #1117 from mprobinson/use-after-free

Fix use-after-free
Set rarch_settings_t * lists to NULL after setting_list_free calls -
messy manual bookkeeping
(XMB) Center messagebox
Merge pull request #1118 from lakkatv/xmb

(XMB) Center messagebox