fix reuse render op

[chiefcll]

parentHasRenderTexture is initialized as false, so this always returns false.

[jfboeve]

depends on: #693 My mistake. This PR has nothing to do with that.

[chiefcll]

This doesn't depend on #693 - They are separate PRs.

Currently the renderer never reuses a RenderOp - on my demo I'm saving ~20% in draw calls.

[jfboeve]

~20% O.o, that is nice.. let's clean the check up a bit:

if (
    params.parentHasRenderTexture === true && 
    this.curRenderOp.framebufferDimensions !== null && 
    params.framebufferDimensions !== null
  ) {
  if(
    this.curRenderOp.framebufferDimensions.w !== params.framebufferDimensions.w || 
    this.curRenderOp.framebufferDimensions.h !== params.framebufferDimensions.h
    ) {
    return false;
  }
}

this decreases the amount if !== null checks