The `displayWidth` and height should never be negative.
The `displayWidth` and height should never be negative.

TukekeSoft/phaser,spayton/phaser,TukekeSoft/phaser,BeanSeed/phaser,photonstorm/phaser,spayton/phaser,mahill/phaser,mahill/phaser,TukekeSoft/phaser,BeanSeed/phaser,photonstorm/phaser