Call gl.getProgramInfoLog before gl.validateProgram

[unconed]

For #1395

Change List

• Call gl.getProgramInfoLog before gl.validateProgram
• Check link status separately from validate status

[ibgreen]

@unconed This looks very good. Happy to land as is, though it would of course always be best to add a test case as well.

I usually try to create a failing test case when I discover an issue, then confirm that a fix makes that test case pass.

Great if you wanted to give it a try, but if too much effort, happy to merge as is.

[unconed]

I'm not familiar enough with the testing set up, I'll leave writing a test case for another kind soul.

[ibgreen]

@unconed Fair enough. For what it's worth I think the test case could quite naturally be placed here: https://github.com/visgl/luma.gl/blob/master/modules/webgl/test/classes/program.spec.js#L29