Prevent crash when removing service task if Core isn't alive

app/src/main/java/org/linphone/core/CoreService.kt

@@ -70,6 +70,7 @@ class CoreService : CoreService() {
     }
 
     override fun onTaskRemoved(rootIntent: Intent?) {
+        if (LinphoneApplication.contextExists()) {
             if (coreContext.core.callsNb > 0) {
                 Log.w("[Service] Task removed but there is at least one active call, do not stop the Core!")
             } else if (!corePreferences.keepServiceAlive) {
@@ -82,6 +83,7 @@ class CoreService : CoreService() {
             } else {
                 Log.i("[Service] Task removed but we were asked to keep the service alive, so doing nothing")
             }
+        }
 
         super.onTaskRemoved(rootIntent)
     }