[MTK] [CONVERGENCE] [ALPS08049534] add NULL checker

check if work_queue_object is NULL

Feature: BT HOST SW
Bug: 328841795
Fix: 328841795
Flag: EXEMPT, minor bug fix
Test: m com.android.btservices
Change-Id: Ia28046095723dcc6a58addf97b9f4d1a41ba0913