RVDSS fix flu subtype behaviour and inf's

[cchuong]

addresses issue(s)

1. Flu subtype percent positivity not null when there are 0 tests
2. Total flu positive tests not being calculated from the subtype totals
3. Infs in the data when there are reported positive tests with 0 total tests.

Summary:

Prerequisites:

• Unless it is a documentation hotfix it should be merged against the dev branch
• Branch is up-to-date with the branch to be merged with, i.e. dev
• Build is successful
• Code is cleaned up and formatted

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

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