SpatialAudio: fix crashes in BluetoothAudioSession

Bug: 224578221
Bug: 214615268
Test: build
Change-Id: I0fd7e0887200e39dc996b0d84de421ec13897e94
diff --git a/bluetooth/audio/utils/aidl_session/BluetoothAudioSession.cpp b/bluetooth/audio/utils/aidl_session/BluetoothAudioSession.cpp
index 37ac967..cdee520 100644
--- a/bluetooth/audio/utils/aidl_session/BluetoothAudioSession.cpp
+++ b/bluetooth/audio/utils/aidl_session/BluetoothAudioSession.cpp
@@ -431,7 +431,9 @@
     std::shared_ptr<PortStatusCallbacks> callback = observer.second;
     LOG(INFO) << __func__
               << " - allowed=" << (allowed ? " allowed" : " disallowed");
-    callback->low_latency_mode_allowed_cb_(cookie, allowed);
+    if (callback->low_latency_mode_allowed_cb_ != nullptr) {
+      callback->low_latency_mode_allowed_cb_(cookie, allowed);
+    }
   }
 }