BT: fix NPE issue in bt stack.

When the mobile phone is connected to the Bluetooth audio, the Bluetooth is restarted abnormally.

Bug: 263323082
BUG: 247439031
Tag: #stability
Test: Manual - Build Floss on Linux

Signed-off-by: wangxianhong <wangxianhong@xiaomi.com>
Change-Id: Ie1fc9eb39ae2bc645f2ec96c7a0d7c369d40c02f
(cherry picked from commit b535b251)
Merged-In: Ie1fc9eb39ae2bc645f2ec96c7a0d7c369d40c02f