Added undefined check processPixelRGB


Phaser.BitmapData#processPixelRGB:

I was getting an undefined error when phaser tried to call setPixel32
using “result.r”:

![pixelprocesserror](https://cloud.githubusercontent.com/assets/1048433/2897762/8d480afe-d589-11e3-9488-d9534fc5be37.png)

With this additional undefined check the problem stopped and I’m able
to run ProcessPixelRGB with all my needed images.