Properly initialize out parameter

Properly initialize out parameter

The MS docs on `SQLColAttribute()`[1] state regarding the
`NumericAttributePtr` parameter:

| Please note that some drivers may only write the lower 32-bit or
| 16-bit of a buffer and leave the higher-order bit unchanged.
| Therefore, applications should initialize the value to 0 before
| calling this function.

[1] <https://docs.microsoft.com/en-us/sql/odbc/reference/syntax/sqlcolattribute-function?view=sql-server-2017>