filetree: restrict keep_directory setting (c86fd23) to Files menu
Prevents the most recent File Browser directory from
being overwritten when ft_load is called from places other
than the Files menu, such as when browsing the Plugins
menu or the Playlist Catalogue (coming from the main menu,
or from the "Add to Playlist" context menu).
Change-Id: Idbdb2d92c6abcc5cca022d3025b48e0cd4b32f17