xwayland: fix GL version check for GLES only devices

We currently bail out early for GLES only devices, and call
epoxy_gl_version() too early for GLES only that will make GLES only
devices return NULL for glGetString(GL_RENDERER).

Let's also add a check to see if we need to recreate the context to
avoid pointless warnings for GLES only devices as suggested by
Olivier Fourdan <ofourdan@redhat.com>.

Fixes: a506b4ec - xwayland: make context current to check GL version
Signed-off-by: Tony Lindgren <tony@atomide.com>
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