r15589: While trying to understand the vuid code I found that security=share is broken

r15589: While trying to understand the vuid code I found that security=share is broken
right now. r14112 broke it, in 3.0.22 register_vuid for security=share returns
UID_FIELD_INVALID which in current 3_0 is turned into an error condition. This
makes sure that we only call register_vuid if sec!=share and meanwhile also
fixes a little memleak.

Then I also found a crash in smbclient with sec=share and hostmsdfs=yes.

There's another crash with sec=share when coming from w2k3, but I need sleep
now.

Someone (jerry,jra?) please review the sesssetup.c change.

Thanks,

Volker