Fix Android stuck when opening from push notification (#1429)

android/app/src/main/java/com/mattermost/rnbeta/MainActivity.java

@@ -1,10 +1,31 @@
 package com.mattermost.rnbeta;
 
+import android.os.Bundle;
+import android.support.annotation.Nullable;
 import com.reactnativenavigation.controllers.SplashActivity;
 
 public class MainActivity extends SplashActivity {
-  @Override
-  public int getSplashLayout() {
-      return R.layout.launch_screen;
-  }
+    @Override
+    protected void onCreate(@Nullable Bundle savedInstanceState) {
+        super.onCreate(savedInstanceState);
+
+        /**
+         * Reference: https://stackoverflow.com/questions/7944338/resume-last-activity-when-launcher-icon-is-clicked
+         * 1. Open app from launcher/appDrawer
+         * 2. Go home
+         * 3. Send notification and open
+         * 4. It creates a new Activity and Destroys the old
+         * 5. Causing an unnecessary app restart
+         * 6. This solution short-circuits the restart
+         */
+        if (!isTaskRoot()) {
+            finish();
+            return;
+        }
+    }
+
+    @Override
+    public int getSplashLayout() {
+        return R.layout.launch_screen;
+    }
 }