Fix 6578735: don't crash system ui when there's no search activity

Because SearchPanelView tracks input even when it's not showing, it
was possible to trigger search with a gesture.

Change-Id: I60f654d279d2ff1799d8a4b69796da8c7e81f3c7

Author: Jim Miller

packages/SystemUI/src/com/android/systemui/SearchPanelView.java

@@ -109,6 +109,7 @@ private void startAssistActivity() {
         mBar.animateCollapse();
         // Launch Assist
         Intent intent = getAssistIntent();
+        if (intent == null) return;
         try {
             ActivityOptions opts = ActivityOptions.makeCustomAnimation(mContext,
                     R.anim.search_launch_enter, R.anim.search_launch_exit);