Fix regression that caused "(I18N_EMPTY_MESSAGE)" sub menus in menus

For top-level roles like "Name" and "Size", the group translation is 0.
In that case, the "group" member of the corresponding RoleInfo struct
must be an empty string. This is expected by the code which generates
Dolphin's menus, which group the top-level roles into a sub menu with
the name "(I18N_EMPTY_MESSAGE)" otherwise. This is a recent regression
caused by 199fabba.

Thanks to Christoph Feck for investigating this issue!

CCBUG: 305228