Created attachment 304078 [details] [review]
gtklistbox: allow unselecting all rows when using GTK_SELECTION_BROWSE

Even using GTK_SELECTION_BROWSE we expect to sometimes not having
selected any row, as the docs says, when i.e. searching or so.
What is enforced is that from any user interaction, only one row can be
selected at once.
But we could allow applications to unselect all rows, for cases when
the application needs to show that something inside the application
invalidated the selection (like when searching, etc).

For user interactions the *_internal methods are used, so it's enough
to remove the check in the public function without affecting the
internal behavior.

ok sorry, that's it what GTK_SELECTION_SINGLE is for....