bp with empty char/varchar column broken

The following worked in 0.91 but is broken as of branch-0_92-839-gd788046.  If we bulk out a table with an empty (but not NULL) char or varchar column that is less than 256 bytes long, 256 spaces get written to the output file for that column.  Which then causes an overflow error if you try to bulk it back in.

I think it was e30a807 that broke it because in src/dblib/bcp.c:_bcp_exec_out we now pass a minimum of 256 as the destlen argument to dbconvert.  We used to pass -2, instructing dbconvert to null terminate without copying anything.

I'm not sure what the correct fix is.  We could possibly pass the lesser of source length and destination length to dbconvert in _bcp_exec_out.  

Here's a reproducer:

$ ./fisql/fisql -Smyserver -Utest
Password:
Changed database context to 'master'.
Changed language setting to us_english.
1>> use tempdb
2>> go
Changed database context to 'tempdb'.
1>> create table testbcp (tmpval varchar(10))
2>> go
1>> insert into testbcp values ('abc')
2>> go
(1 rows affected)
1>> insert into testbcp values ('')
2>> go
(1 rows affected)
1>> exit
$ ./freebcp tempdb.dbo.testbcp out tmp.bcp -Smyserver -Utest -P***** -c

Starting copy...
2 rows copied.
$ perl -nle 'print length($_);' < tmp.bcp
3
256
$ ./freebcp tempdb.dbo.testbcp in tmp.bcp -Smyserver -Utest -P***** -c

Starting copy...
Msg 20049, Level 4
Data conversion resulted in overflow

1 rows copied.

________________________________________
Craig A. Berry
mailto:[email protected]

"... getting out of a sonnet is much more
 difficult than getting in."
                 Brad Leithauser