smb_open_sub() will now create the msgbase if hasn't been created yet.

I noticed that more than one caller of smb_open_sub() would not call
smb_create() if the sub had not been previously "created" and in some of the
instances where they did call smb_create(), if create failed, the message base
was errorneously left open. So just do the create here to elmiinate the chance
of error (forgetting) and redundancy of logic.