Add and use mixxx::Bpm::valueOr()

[uklotzde]

Follow-up of #4165 to resolve some FIXME comments.

[coveralls]

Pull Request Test Coverage Report for Build 1101432505

• 0 of 21 (0.0%) changed or added relevant lines in 2 files are covered.
• 80 unchanged lines in 3 files lost coverage.
• Overall coverage increased (+0.003%) to 26.014%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/library/basetracktablemodel.cpp	0	3	0.0%
src/library/dlgtrackinfo.cpp	0	18	0.0%

Files with Coverage Reduction	New Missed Lines	%
src/library/dlgtrackinfo.cpp	1	0%
src/controllers/scripting/controllerscriptenginebase.cpp	36	40.19%
src/util/cmdlineargs.cpp	43	72.73%

Totals
Change from base Build 1087078133:	0.003%
Covered Lines:	20008
Relevant Lines:	76913

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💛 - Coveralls

[mr-smidge]

FWIW, I tried performing an "Entire music library" export to Engine Prime using this branch, and it completed successfully. The previous codebase would occasionally trigger assertion failures in Bpm::value() for such an operation if there were tracks where analysis was not valid.

So gets my vote 👍.

[Holzhaus]

I'm open to it, but the resulting double is not undefined, it's zero. Should it be valueOrZero? Unsure about that.

[uklotzde]

I'm open to it, but the resulting double is not undefined, it's zero. Should it be valueOrZero? Unsure about that.

Good point! On the value level there is no undefined, which would otherwise be NaN.

[uklotzde]

An optional that wraps always valid BPM values would be more idiomatic. A value of 0.0 is valid for some rare, ambient, beatless tracks. Let's defer this until we rewrite in Rust ;)

[Holzhaus]

Thanks, looks good.