Fix "fileActions.currentFile" not set before using it

When an empty area of a file row was clicked and the "Details" action
was executed "fileActions.currentFile" was not guaranteed to be set to
the appropriate object (it depended on the previous actions of the
user), so when it was used by "getCurrentMimeType()" and other
FileActions functions they may not work as expected. Now it is
explicitly set to the appropriate value before its use.

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