Bug#920462: libgl1-mesa-dri 18.3.2 breaks certain proprietary steam games

I can confirm that mesa 18.3.4-2 fixes the issue.

Bug#920462:

< util_blitter_generate_mipmap: Assertion `!util_format_has_stencil(desc)' failed. I think debian Mesa packages should disable these assertions, that was disabled before in 18.2.8 and earlier... Maybe it is leftover because of Meson build system now, that have assertions enabled by default, so