Getting bytea results via SQLGetData

Hi, there!

It seems there's a bug with fetching bytea (SQL_VARBINARY) columns via
SQLGetData() as SQL_C_CHAR, you always get zero-length result.
I'm using unixODBC-1.8.12, but that code is the same with code
of driver in postgres distribution.

In convert.c in function copy_and_convert_field there is a special case
for such a values, but it works improperly. Without this case, when
bytea data is processed as anything else everything seems to work fine.
Driver receives pretty good escaped data i think there is no need to do
something with it.

Here is a patch for convert.c.

/Constantin