Add workaround for Unicore GLL firmware issue

[semuadmin]

pynmeagps Pull Request Template

Description

1. Add workaround for Unicore UM9* firmware error, which creates malformed NMEA GLL sentences (-ve latitude or longitude).

Fixes # Issue where NMEA GLL sentences would parse to an incorrect latitude or longitude value due to a firmware error in Unicore UM9* series receivers.

Testing

Please test all changes, however trivial, against the supplied pytest suite tests/test_*.py. Please describe any test cases you have amended or added to this suite to maintain >= 99% code coverage.

• test_stream.py updated

Checklist:

• I agree to abide by the code of conduct (see CODE_OF_CONDUCT.md).
• My code follows the style guidelines of this project (see CONTRIBUTING.md).
• I have performed a self-review of my own code.
• I have commented my code, particularly in hard-to-understand areas.
• I have made corresponding changes to the documentation.
• (if appropriate) I have added test cases to the tests/test_*.py unittest suite to maintain >= 99% code coverage.
• I have tested my code against the full tests/test_*.py unittest suite.
• My changes generate no new warnings.
• Any dependent changes have been merged and published in downstream modules.
• I have signed my commits.
• I understand and acknowledge that the code will be published under a BSD 3-Clause license.