egl_dri2: set ctx->WindowRenderBuffer

Set ctx->WindowRenderBuffer to EGL_BACK_BUFFER.  As EGL_WINDOW_BIT of a
config is set only when there is dri_double_buffer, that makes sure
window surfaces are always double-buffered and contexts will render to
the back buffer.

Reviewed-by: Chad Versace <chad@chad-versace.us>
1 file changed