fix: Fix output of calculateShards() when all tests are filtered out

[doodla]

When all tests were filtered out, it would throw an error Invalid shard time.

Test Plan

How do we know the code works?
Create a test apk with one test class with an annotation, and @Ignored.
Filter the tests using that annotation.

Console should print out No tests for ... instead of crashing with Invalid shard time.

Checklist

Couldn't find existing tests for this class.

[github-actions]

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[doodla]

recheck

[doodla]

I have read the CLA Document and I hereby sign the CLA

[Sloox]

@flank-it

[github-actions]

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