_mssql: get_resuls(): Handle dbcolname() returning NULL column name.
_mssql: get_resuls(): Handle dbcolname() returning NULL column name.

This usually happens when the connection to the server is interrupted
and was causing a segmentation fault later.

Fixes #271

Aloomaio/pymssql,ramiro/pymssql,pymssql/pymssql,ramiro/pymssql,pymssql/pymssql,Aloomaio/pymssql,JimDennis/pymssql,ramiro/pymssql,JimDennis/pymssql,JimDennis/pymssql,Aloomaio/pymssql