Check $strictNullComparison outside of loops

[ConnectGrid]

Might be considered a micro-optimization, but for large sheets, it could make a difference in performance. Only check the $strictNullComparison condition once, not for every single cell loop.

This is:

• a bugfix
• a new feature
• refactoring
• additional unit tests

Checklist:

• Changes are covered by unit tests
  • Changes are covered by existing unit tests
  • New unit tests have been added
• Code style is respected
• Commit message explains why the change is made (see https://github.com/erlang/otp/wiki/Writing-good-commit-messages)
• CHANGELOG.md contains a short summary of the change and a link to the pull request if applicable
• Documentation is updated as necessary

Why this change is needed?

Instantiating Worksheets from an array are currently less than optimal due to checking a boolean condition on every single cell loop.

[oleibman]

Nothing more to discuss.

[oleibman]

Thank you for your contribution.