Code review comment for lp:~afrantzis/mir/fix-1454201-usc-crash-for-0.13

Seems to work, but I'm not sure why.

Unfortunately...

$ bin/mir_unit_tests --gtest_filter=GLRenderer.*:DemoRenderer.*
...
[ FAILED ] 5 tests, listed below:
[ FAILED ] GLRenderer.disables_blending_for_rgbx_surfaces
[ FAILED ] GLRenderer.binds_for_every_primitive_when_tessellate_is_overridden
[ FAILED ] GLRenderer.opaque_alpha_channel
[ FAILED ] GLRenderer.generates_alpha_channel_content
[ FAILED ] DemoRenderer.detects_embellishments_on_renderables