Fix duplicated filename in reference when using write_reference_line_numbers

[agenestar]

Fixes #344

[coveralls]

Pull Request Test Coverage Report for Build 1917278e94abdf061baae8c4134ebced3c78fd08-PR-345

• 6 of 6 (100.0%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+0.07%) to 89.533%

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Totals
Change from base Build 2ebe8066d6309ea2d810beb93e38433fef6f5071:	0.07%
Covered Lines:	556
Relevant Lines:	621

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💛 - Coveralls

[agenestar]

Thanks @maennchen for your help :)