Add safety mechanism for cases when prediction scores are 0 for all c…

[ludvigla]

…ell types

Description

This PR includes a fix for an edge case where the predicted cell types scores were 0 in AnnotateCells with method "method". This triggers a downstream crash because those cells will be missing from the output.

Fixes: PNA-3051

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• This change requires a documentation update.

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce it when relevant.

PR checklist:

• My changes generate no new warnings.
• I have added tests that prove my fix is effective or that my feature works.
• I have documented any significant changes to the code in CHANGELOG.md