Add bounds check in avdt_scb_act.cc

Bug: 242535997
Test: BT unit tests, validated against researcher POC
Tag: #security
Ignore-AOSP-First: Security
Change-Id: Id3b665da0214e3c93f277e31077214fcd1d936e7
(cherry picked from commit 789d4bc6)
Merged-In: Id3b665da0214e3c93f277e31077214fcd1d936e7