honor seed=0 by checking if seed is none instead of using or operator

[fyordan]

This is probably why seed wasn't being honored, since 0 or random will be random everytime, its better to check explicitly for None.

[netlify]

✅ Deploy Preview for catanatron-staging canceled.

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[coveralls]

Pull Request Test Coverage Report for Build 4466013805

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 95.728%

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Files with Coverage Reduction	New Missed Lines	%
catanatron_core/catanatron/state.py	2	97.17%

Totals
Change from base Build 4462284319:	-0.1%
Covered Lines:	1367
Relevant Lines:	1428

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💛 - Coveralls

[bcollazo]

Nice! LGTM!