LeAclManagerFacade: Check per_connection_events

Avoid a segmentation fault if there was no previously connected device.

Bug: 230123996
Test: cert/run
Tag: #gd-refactor
Change-Id: Ibcc4469498d2e17e49a51d4e9b59ba38919244a2
Merged-In: Ibcc4469498d2e17e49a51d4e9b59ba38919244a2
(cherry picked from commit 0ffa964fd59157f0fec39786a840ee387959ad49)