Settings crashed by a null worker

-Add worker checker
-Add test case

Bug: 153356562
Test: make -j42 RunSettingsRoboTests
Change-Id: I129ff63a48b3785aacc846fe1dd67a926a8e5e1f

tests/robotests/src/com/android/settings/media/MediaOutputIndicatorSliceTest.java

@@ -21,7 +21,9 @@ import static com.android.settings.slices.CustomSliceRegistry.MEDIA_OUTPUT_INDIC
 
 import static com.google.common.truth.Truth.assertThat;
 
+import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.Mockito.doReturn;
+import static org.mockito.Mockito.never;
 import static org.mockito.Mockito.spy;
 import static org.mockito.Mockito.verify;
 import static org.mockito.Mockito.when;
@@ -190,6 +192,14 @@ public class MediaOutputIndicatorSliceTest {
         assertThat(metadata.isErrorSlice()).isTrue();
     }
 
+    @Test
+    public void onNotifyChange_noWorker_doNothing() {
+        sMediaOutputIndicatorWorker = null;
+        mMediaOutputIndicatorSlice.onNotifyChange(new Intent());
+
+        verify(mContext, never()).startActivity(any());
+    }
+
     @Test
     public void onNotifyChange_withActiveLocalMedia_verifyIntentExtra() {
         when(mMediaController.getSessionToken()).thenReturn(mToken);