Fix #172, Move DS_TableFindMsgID lookups out of DS_AddMidCmd conditions

[chillfig]

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name: FSW Code Change
about: Flight Software code changes
labels: fsw

Description of Change

Helps DS satisfy JPL Rule 19 and MISRA C:2012 Rule 13.4

• Replace the single FilterTableIndex with two named locals.
  • ExistingIndex [index of the MID if DS already tracks it]
  • UnusedIndex [first free filter table slot]

Both lookups now run as plain statements ahead of the if/else logic, and the conditions only test the results.

• Initialize both to DS_INDEX_NONE instead of 0, since 0 is a valid filter table index.
• Guard the lookups with a check for a filter table since DS dereferences the filter table pointer at lookup, so the lookups must only run when a table is loaded.

Linked Issue

Closes #172

Requirements Impact

• Requirement ID(s):
• Requirements updated as necessary
• Existing requirements are still satisfied by this change

Testing Evidence

CI shows maintained coverage

Unit Tests (UT Assert)

CI shows maintained coverage

COSMOS Test Suite

N/A

Areas of Expertise Touched

• ASTRO
• CI/CD
• COSMOS
• Cybersecurity
• Docker
• EDS
• Git
• PSPs
• SBN
• SMP
• Tables
• TSN
• Unit Tests
• Other

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Author Checklist

• Linked GitHub issue is referenced above
• Code has been formatted with .clang-format
• Static analysis workflows ran and passed
• Unit tests (UT Assert) updated/added to cover code changes
• Unit test workflows ran and passed
• COSMOS test suite was run; tests updated/added if relevant changes were made
• Requirements have been reviewed; updated or confirmed still satisfied (see above)
• Testing evidence is included above
• Self-review of the diff completed

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Reviewer Checklist

• Code logic is correct and matches the stated intent
• Code is readable, maintainable, and follows project conventions (ask your lead if you are unsure of where to find these conventions)
• .clang-format has been applied
• Static analysis results reviewed and acceptable
• The change has been exercised by the unit tests (not just that tests pass — the new/changed code paths are actually covered)
• COSMOS test suite was executed against this change and results reviewed (or confirmed N/A with justification)
• Reviewer has independently verified the change behaves as described (e.g., by running the tests locally, reviewing CI output in detail, or performing additional ad-hoc testing as warranted)
• Memory safety reviewed (allocation, bounds, lifetime, stack usage)
• Requirements impact reviewed and appropriate
• Error handling is appropriate
• Appropriate Expert areas have been reviewed

Reviewer Testing Notes