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 199fabbaa8d8a12fb49e4c9922c38ec8b033923c.

Thanks to Christoph Feck for investigating this issue!

CCBUG: 305228
(cherry picked from commit 168d0511c754008cc679589566d961beb9f6cc10)