Summary

Some queries can return NULL values (mainly in replication scenarios). To prevent potential issues, this PR ensures values are set whenever the final query delivers a NULL.

Test Plan

1. Compile Branch.
2. Install on a host running MSSQL and verify everything is running as expected.

Additional Information

Summary by cubic

Handle MSSQL NULL results across the Windows plugin collectors by defaulting numeric fields to 0 and strings to empty, preventing bad metrics and errors, especially in replication and status queries.

• Bug Fixes
  • Set safe defaults when SQL_NULL_DATA is returned in transactions, locks, waits, replication, job status, user connections, DB list, and permission/status queries.
  • Updated fill_long_value to treat NULL sizes as 0.
  • Used separate length variables to correctly detect NULLs for DB state and readonly flags.

^{Written for commit 09545b3. Summary will update automatically on new commits.}