fix: problem to identify new sequences

[pythonbrad]

The problem come from an incomplete implementation at 7b3d09c (#44).
It's most observed for sequences of one character (eg. a -> x).

[coveralls]

Pull Request Test Coverage Report for Build 5990419163

• 22 of 22 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.01%) to 99.196%

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Totals
Change from base Build 5939982376:	0.01%
Covered Lines:	617
Relevant Lines:	622

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💛 - Coveralls