Steps to reproduce:
1. Go to the store tab, on the top there is a category dropdown, select
free-to-play
2. Select any free-to-play game from the list that doesn't support Linux
3. Click the green "play game" button
4. An error dialog tells you that "this game is not available for your current
platform"

With r600g the dialog is garbled, with llvmpipe it's OK.

Report on steam issue tracker:
https://github.com/ValveSoftware/steam-for-linux/issues/2732