Fix crash when Data Source starts with a comma

[Midhunnnk]

Fixes #3110
this PR fixes a crash in ADP.IsEndpoint(...) caused by an unsafe call to LastIndexOf('\\', length - 1, length - 1) when the Data Source in the connection string starts with a comma (e.g. "Data Source=,").

When length == 0, the method would previously throw an ArgumentOutOfRangeException.

---Fix
Added a defensive check to ensure length > 0 before calling LastIndexOf, which prevents invalid index access.

--- Tests

• Added a new unit test: ConnectionString_WithOnlyComma_ShouldNotThrow
• The test confirms that the exception is no longer thrown
• Verified the test fails without the fix and passes with it

This is my first open-source contribution — excited to be part of the project! Let me know if you'd like any changes.

[Midhunnnk]

@dotnet-policy-service agree

[paulmedynski]

Great fisrt open-source contribution! Little bugs like these can be very frustrating for users, so we appreciate you taking the time to fix one :)

[paulmedynski]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[Midhunnnk]

@paulmedynski Thank you for the feedback, it helps a lot 😄 I've updated the test name and replaced Record.Exception with Assert.Throws() as suggested. Let me know if you'd like anything else adjusted — happy to improve further!

[cheenamalhotra]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[paulmedynski]

Changes look great - thanks!

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 0.00%. Comparing base (1247ca4) to head (ccbf510).
Report is 11 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #3250       +/-   ##
==========================================
- Coverage   72.69%       0   -72.70%     
==========================================
  Files         303       0      -303     
  Lines       59718       0    -59718     
==========================================
- Hits        43414       0    -43414     
+ Misses      16304       0    -16304     

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