files.c: Init char *name to NULL
    
    Merges:
    https://pagure.io/libuser/issue/27
    
    This is mostly to silence coverity warnings. "enum lu_entity_type" has
    three values and several places in the code follow logic as:
    
    char *name;
    if ent->type == user:
            name = foo()
    if ent->type == group
            name = bar()
    g_assert(name != NULL)
    
    it shouldn't be possible for ent->type to be anything else but in the
    odd case it is, initializing name to NULL will ensure that name will be
    still NULL after the code falls through the conditions and at least the
    behaviour is defined.