Hide favourite icon in details view if favourite action is not available

When the favourite icon in the details view is clicked the "Favorite"
action is triggered. However, if the action name given to
"triggerAction" is not found then the "Download" action is triggered
instead. As the "Favorite" action is not available in some file lists
(like "Recents") the "Download" action was executed instead in those
cases, which was a strange behaviour. Now the favourite icon is
hidden if its action is not available.

Signed-off-by: Daniel Calviño Sánchez <danxuliu@gmail.com>