Fix null pointer on dismissing suggestion.

Add null check for context when getting the suggestion identifier, since
this is called from async task and context might becomes null.

Change-Id: If17036803de1634891b659a4fc6bd4b8a76ef5fb
Fix: 36605386
Test: make RunSettingsRoboTests

tests/robotests/src/com/android/settings/dashboard/suggestions/SuggestionFeatureProviderImplTest.java

@@ -107,6 +107,15 @@ public class SuggestionFeatureProviderImplTest {
                 .isNotEmpty();
     }
 
+    @Test
+    public void getSuggestionIdentifier_nullContext_shouldNotCrash() {
+        final Tile suggestion = new Tile();
+        suggestion.intent = new Intent()
+            .setClassName(RuntimeEnvironment.application.getPackageName(), "123");
+        assertThat(mProvider.getSuggestionIdentifier(null, suggestion))
+            .isNotEmpty();
+    }
+
     @Test
     public void dismissSuggestion_hasMoreDismissCount_shouldNotDisableComponent() {
         when(mSuggestionParser.dismissSuggestion(any(Tile.class), anyBoolean()))
@@ -120,7 +129,6 @@ public class SuggestionFeatureProviderImplTest {
         verify(mContext, never()).getPackageManager();
     }
 
-
     @Test
     public void dismissSuggestion_noContext_shouldDoNothing() {
         mProvider.dismissSuggestion(null, mSuggestionParser, mSuggestion);