s4:registry - "reg_ldb_pack_value" - provide workarounds when the server receives...

s4:registry - "reg_ldb_pack_value" - provide workarounds when the server receives non-standard data.

For now we reset/delete the "data" attribute. Anyway there is the need to find
a better solution (we probably want to change the format and save all data as
we got it like Windows itself does).

These workarounds are needed since for example the Windows 2000 Registry Editor
initialises empty REG_SZ strings with content '\0' and length 1 (not a valid
UTF16 sequence - "convert_string_talloc" breaks). So we simply reset/delete the
"data" attribute which works (no content).