cmgen should support tiled EXR images

[prideout]

We need to either (a) contribute a high-level utility function to tinyexr, or (b) write or own tile assembler.

For inspiration here is a tiled-to-scanline converter:
https://github.com/syoyo/tinyexr/blob/b9f100e4a9ab80389b151fc2b53731d31035d327/test_tinyexr.cc#L75

See also:
syoyo/tinyexr#93

[prideout]

Now that we've updated tinyexr which now handles tiled images, this issue should be trivial to close (just remove an assert)

#197

[romainguy]

Should I just remove the assert then? I preserved it just in case.

[romainguy]

I just checked and TinyEXR does support tiled images in the function we call now.

[prideout]

Correct, we can simply remove the assert.