Add null check for mIntent in ZenRulePreference to avoid potential crash risk

Bug: 244120502

Test: manual test, ZenRuleScheduleHelperTest for unit test.
Change-Id: Ib7338253783bb09b84b629f2dd891292d82f28b2

src/com/android/settings/notification/zen/ZenRulePreference.java

@@ -91,7 +91,9 @@ public class ZenRulePreference extends PrimarySwitchPreference {
 
     @Override
     public void onClick() {
-        mContext.startActivity(mIntent);
+        if (mIntent != null) {
+            mContext.startActivity(mIntent);
+        }
     }
 
     @Override