[Wi-Fi] Prevent fatal exception for null intent action

Intent action may be null.

Bug: 139020487
Test: WifiScanModeActivityTest
      WifiNoInternetDialogTest
      WifiDppConfiguratorActivityTest
      WifiDppEnrolleeActivityTest
Change-Id: Ie6119a86aaee1a6b40710705a0ea7d92c24736d6

tests/robotests/src/com/android/settings/wifi/WifiScanModeActivityTest.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License
+ */
+
+package com.android.settings.wifi;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.robolectric.Robolectric;
+import org.robolectric.RobolectricTestRunner;
+
+@RunWith(RobolectricTestRunner.class)
+public class WifiScanModeActivityTest {
+    @Test
+    public void launchActivity_noIntentAction_shouldNotFatalException() {
+        WifiScanModeActivity wifiScanModeActivity =
+                Robolectric.setupActivity(WifiScanModeActivity.class);
+    }
+}