Fix #1461, Move data lock to inside of if block

[thnkslprpt]

Checklist

• I reviewed the Contributing Guide.
• I signed and emailed the appropriate Contributor License Agreement to GSFC-SoftwareRelease@mail.nasa.gov and copied cfs-program@lists.nasa.gov.

Describe the contribution

• Fixes Reduce scope of lock to within if statement in CFE_SB_ReleaseMessageBuffer #1461
  • Data lock moved inside the if block (lock is not needed if the if block condition doesn't evaluate to true).

Testing performed
GitHub CI actions (incl. Build + Run, Unit Tests etc.) all passing successfully.

Expected behavior changes
Data lock will not occur in the (unexpected) case of an error return from CFE_SB_ZeroCopyBufferValidate(), which is fine as no data would be accessed/amended in that case anyway.

Contributor Info
Avi @thnkslprpt