Bugfix 1552: Set row_count/rows to None in get_description/get_info and batch versions thereof if symbol is pickled

[alexowens90]

Reference Issues/PRs

Fixes #1552

The row_count field of the get_description return value (and equivalent on V1 API, and the return value of get_num_rows) was misleadingly set if the symbol was pickled. Now it will be None in this case.

Causes (tiny) API change for V2, so wait to merge until 5.0.0