efl_fileselector_entry: do not crash on a invalid model

efl_fileselector_entry: do not crash on a invalid model

something is happening during shutdown, when a fileselector was created
before. This is ending up in a strcmp to a NULL ptr, which crashes, with
the now, we ensure that we are not crashing anymore, when that is
happning.

TO solve this properly we should really fix the cause of a invalid model
beeing returned, however, i do not feel compftable doing that so short
before a release.

Reviewed-by: Stefan Schmidt <stefan@datenfreihafen.org>
Differential Revision: https://phab.enlightenment.org/D11762