Fix onHostPause crash on Android (#7812)

* Fix onHostPause crash on Android

* Update NavigationModule.java

Author: yogevbd

lib/android/app/src/main/java/com/reactnativenavigation/react/NavigationModule.java

@@ -59,7 +59,9 @@ public NavigationModule(ReactApplicationContext reactContext, ReactInstanceManag
             @Override
             public void onHostPause() {
                 super.onHostPause();
-                UiUtils.runOnMainThread(() -> navigator().onHostPause());
+                UiUtils.runOnMainThread(() -> {
+                    if (activity() != null) navigator().onHostPause();
+                });
             }
 
             @Override