vulkan/wsi/x11: don't crash on null visual
vulkan/wsi/x11: don't crash on null visual

When application window closed unexpectedly due to
lost window visualtypes getting invlaid parameters
which is causing a crash. Necessary check is added
to prevent the crash.

Reviewed-by: Jason Ekstrand <68c46a606457643eab92053c1c05574abb26f861@jlekstrand.net>
Cc: "13.0" <59f39c0db42d4479a46b02d4d2bc11120e37bb44@lists.freedesktop.org>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler