Fix windows warnings in LibUtilities and StdRegions

Issue/feature addressed

Clean up some compiler warnings from the Windows build.

Proposed solution

Adjust code to avoid ambiguous statements, or adjust logic to avoid the warnings appearing.

Checklist

• Functions and classes, or changes to them, are documented.
• User guide/documentation is updated.
• Changelog is updated.
• Suitable tests added for new functionality.
• Contributed code is correctly formatted. (See the contributing guidelines).
• License added to any new files.
• No extraneous files have been added (e.g. compiler output or test data files).