Bisection should not produce zero-length commit ranges

[andrewpollock]

Describe the bug
#1984 surfaced that the bisection performed for OSS-Fuzz sometimes produces a zero-length range, which is invalid
See the list of records at #1984 (comment)

Expected behaviour
Such ranges should not be produced.

[andrewpollock]

https://github.com/google/osv.dev/blob/master/docker/worker/oss_fuzz.py is where the action is

[github-actions]

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