12.4 Release notes: Improve ocs_fc entry

• Split entry into multiple entries sorted chronologically by commit date.
• Increase number of use-after-free bugs fixed from 1 to 2.
• Reduce number of memory leaks fixed from 'some' to 1 (I could not find more in the logs).
• Add a possible null pointer dereference fix.
• Add gitref notes.

Approved by: re (gjb, implicit)