[BUG] [GLSL] [Nexus Player] Single-iteration loop changes the rendered image

The fragment shader files, screenshots, reproduction steps and platform info are available here:
https://github.com/mc-imperial/shader-compiler-bugs/issues/50

You can reproduce this on the Nexus Player via WebGL:

http://htmlpreview.github.io/?https://github.com/mc-imperial/shader-compiler-bugs/blob/master/nexus-player/wrong_images/large-v100-6a34d929ab771b65_inv_variant_25/webgl_viewer_recipient.html

http://htmlpreview.github.io/?https://github.com/mc-imperial/shader-compiler-bugs/blob/master/nexus-player/wrong_images/large-v100-6a34d929ab771b65_inv_variant_25/webgl_viewer_variant.html

Hi Paul,

We have tested the fragment shader on the Nexus Player running the latest version of our drivers and we could not reproduce the problem, therefore the problem must have been fixed in subsequent driver updates.

Kind Regards,
Shaun