Revert "Fix a bug in MaskInverse.Filter(). (#6)"

[elvizlai]

This reverts commit 4892f147ae6408ffccaf5eeecd3b0572b17e59aa.

[coveralls]

Pull Request Test Coverage Report for Build 41

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.1%) to 86.97%

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Totals
Change from base Build 39:	-0.1%
Covered Lines:	1435
Relevant Lines:	1650

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💛 - Coveralls

[elvizlai]

As #8 , Close this.