Bug 828480 - Add null check for mSuggestionsOptInPrompt. r=mfinkle

mobile/android/base/awesomebar/AllPagesTab.java

@@ -627,6 +627,14 @@ public class AllPagesTab extends AwesomeBarTab implements GeckoEventListener {
     }
 
     private void setSuggestionsEnabled(final boolean enabled) {
+        // Clicking the yes/no buttons quickly can cause the click events be
+        // queued before the listeners are removed above, so it's possible
+        // setSuggestionsEnabled() can be called twice. mSuggestionsOptInPrompt
+        // can be null if this happens (bug 828480).
+        if (mSuggestionsOptInPrompt == null) {
+            return;
+        }
+
         // Make suggestions appear immediately after the user opts in
         primeSuggestions();