fix: Allow empty tags in BAM header

[mrvollger]

Hello,

I recently ran into an issue where BAM files with empty tags in their header fail with rust-htslib whereas they work fine with samtools and even with quickcheck within samtools. For example a barcode tag without a value (BC:) within @RG would throw an unwrap error when using to_hashmap.

This just needs a one character change in the regex + -> *, so hopefully wont cause any issues or changes in compatibility.

Thanks for considering!
Mitchell

[coveralls]

Pull Request Test Coverage Report for Build 4661386895

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 78.962%

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Totals
Change from base Build 4562489535:	0.0%
Covered Lines:	2267
Relevant Lines:	2871

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💛 - Coveralls

[johanneskoester]

thanks a lot!