user-switching: Make sure all exit paths have return values
    
    The openSUSE Build Service raises a flag for
    
    [   55s] I: Program returns random data in a function
    [   55s] E: gdm no-return-in-nonvoid-function gdm-common.c:850
    [   55s] E: gdm no-return-in-nonvoid-function gdm-user-switching.c:597
    
    This can happen when CONSOLEKIT is disabled (As is newly the case) and
    LOGING_RUNNING would return false.
    
    Based on a patch by Dominique Leuenberger
    
    https://bugzilla.gnome.org/show_bug.cgi?id=744787