bwauth: Ignore bandwidth file lines with "vote=0"

[juga0]

so that the relays that would be "excluded" from the bandwidth
file because of something failed can be included to diagnose what
failed, without still including these relays in the bandwidth
authorities vote.

Closes #29806.

[coveralls]

Pull Request Test Coverage Report for Build 4307

• 5 of 5 (100.0%) changed or added relevant lines in 1 file are covered.
• 12 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.01%) to 60.304%

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Files with Coverage Reduction	New Missed Lines	%
src/feature/dirauth/shared_random.c	3	85.64%
src/feature/dirauth/dirvote.c	9	64.79%

Totals
Change from base Build 4293:	-0.01%
Covered Lines:	42858
Relevant Lines:	71070

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💛 - Coveralls

[teor2345]

Squashed and now in #820.