[4.0.0-rc.5] Mask rendered wrong when camera has viewport set

[leemanhopeter]

Version

• Phaser Version: 4.0.0-rc.5

Description

If a container is masked and the main camera has its viewport set, then the container will be rendered incorrectly

Example Test Code

https://phaser.io/sandbox/o1rzdqof

In the example above, the container is rendered wrong. To see what it should look like, comment out line 16 which sets the mask of the container.