When exiting the *Completions* buffer, C-g and q seem not to send the
user back to minibuffer.  This introduces friction via uncertainty,
because you don't know where the active point will land, so you have to
manually switch back.  This command adds and binds command that ensure
the minibuffer is always selected once it is closed or unfocused.  I
think this is an absolute improvement, so there is no option to reset
this behaviour.