Blender Git Loki

After chatting with Broken about grs comments on the default behavior
of the nodes, I realized I had strayed from the path of enlightened blending
by causing the math node to create an output the size of the larger of the
two inputs.

It has been corrected create the output the size of the
first image, and in its abscense the second image. In the event of
nether input containing image data the node does not function. I also
added some early out checks at the beginning of the function to speed it
up a tad in these cases and commented the code a bit more.