Recover from PyLint raising messages at character "-1"

Summary: Fixes T9257. For some messages, PyLint can raise at "character -1", which we don't allow since we don't consider it to make sense.

Test Plan:

• Added failing unit test from T9257.
• Applied patch.
• Test now passes.

Reviewers: joshuaspence, chad

Reviewed By: joshuaspence, chad

Maniphest Tasks: T9257

Differential Revision: https://secure.phabricator.com/D13991