Projection does not work with canvas textures

[jimbauwens]

Similar to the issue with video textures, canvas textures do not work as the dimensions are not properly computed in computeScaledDimensions.

This is easily solvable by using:

 const sourceWidth = texture.image.naturalWidth || texture.image.videoWidth || texture.image.clientWidth;
 const sourceHeight = texture.image.naturalHeight || texture.image.videoHeight || texture.image.clientHeight;

However, it might be cleaner to add a utility function to fetch these source dimensions, as some other code seems to fetch dimensions too (e.g. in addLoadListener).

[marcofugaro]

Hey, no need for the utility function, just the two lines you proposed are enough. Could you do a PR?

[jimbauwens]

Ok, see #23 :)