Fix #72 + Fix #206, Correct iteration bug in TO_LAB_RemoveAllCmd

[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 Mark empty slots with invalid msgid, and don't try to unsubscribe all on them #72
• Fixes Iteration missing for SubEntry in TO_LAB_RemoveAllCmd() #206
  • both issues actually had the same root cause which was the missing iteration of SubEntry, which caused the TO_LAB_RemoveAllCmd command try to to unsubscribe from the same entry TO_LAB_MAX_SUBSCRIPTIONS times

Testing performed
Tested with local cFS build to confirm prior and post-fix behavior is as described above.

Expected behavior changes
App will correctly iterate through the subs table now.

System(s) tested on
Debian 12 using the current main branch of cFS bundle.

Contributor Info
Avi Weiss   @thnkslprpt