RenderImg: Return the Image2grey

Another commented method.

Signed-off-by: Celelibi <celelibi@gmail.com>
RenderImg: Don't crash when the image don't load

The class Image don't say much when it fail to load, it just don't set
the width and height.

Signed-off-by: Celelibi <celelibi@gmail.com>