Buffer overflow in cursor create_name_map

[juliuszsompolski]

Function create_name_map used a static buffer szName[300] for the column name in call to SQLDescribeColW. That function would truncate the column name to the size of the provided buffer, but return the actual length of the column name in the &cchName return parameter.
That cchName output was used to compute cbName parameter for the call to TextBufferToObject(enc, szName, cbName). When the actual column name was longer than the buffer, cbName was to big, and was causing a buffer overflow, resulting in crashes, invalid data, or errors.

Fix this by making szName a dynamic buffer. This buffer overflow is very similar to the one fixed in mkleehammer#881. I check through the rest of the code base, and I don't see more places with static buffers that could have a similar issue.

Upstream PR: mkleehammer#931