We used to store smbXsrv_tcon_global.tdb records in two steps,
first we created a record in order to allocate the tcon id.
The temporary record had a NULL share_name, which translated
into 0 bytes for the string during ndr_push_smbXsrv_tcon_global0.

The problem is that ndr_pull_smbXsrv_tcon_global0 fails on
this with something like:

Invalid record in smbXsrv_tcon_global.tdb:key '2CA0ED4A' ndr_pull_struct_blob(length=85) - Buffer Size Error

The blob looks like this:

[0000] 00 00 00 00 01 00 00 00   00 00 00 00 00 00 02 00   ........  ........
[0010] 00 00 00 00 4A ED A0 2C   4A ED A0 2C 00 00 00 00   ....J.., J..,....
[0020] F8 4B 00 00 00 00 00 00   00 00 00 00 FF FF FF FF   .K......  ........
[0030] 4D 59 9B 9F 83 F4 35 20   36 D2 B0 82 62 68 D9 01   MY....5 6...bh..
[0040] 00 00 00 00 00 00 00 00   00 00 00 00 00 00 00 00   ........  ........
[0050] 00 00 00 00 00                                      .....