libxl: initialize sdl.opengl defbool in libxlMakeVfb
libxl: initialize sdl.opengl defbool in libxlMakeVfb

Commit bf32462b missed initializing sdl.opengl.  Without the
initialization, libvirtd will be terminated by an assert from libxl:

Assertion `!libxl_defbool_is_default(db)' failed.

Reported-by: Olaf Hering <ded022db89399a060a39da31922f173c6556c2d9@aepfle.de>

taget/libvirt,eskultety/libvirt,jardasgit/libvirt,nertpinx/libvirt,jfehlig/libvirt,rlaager/libvirt,fabianfreyer/libvirt,zippy2/libvirt,andreabolognani/libvirt,taget/libvirt,datto/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,taget/libvirt,taget/libvirt,libvirt/libvirt,rlaager/libvirt,jardasgit/libvirt,eskultety/libvirt,eskultety/libvirt,VenkatDatta/libvirt,zippy2/libvirt,zippy2/libvirt,fabianfreyer/libvirt,crobinso/libvirt,olafhering/libvirt,jardasgit/libvirt,datto/libvirt,rlaager/libvirt,olafhering/libvirt,olafhering/libvirt,andreabolognani/libvirt,jfehlig/libvirt,crobinso/libvirt,olafhering/libvirt,agx/libvirt,eskultety/libvirt,crobinso/libvirt,libvirt/libvirt,rlaager/libvirt,VenkatDatta/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,andreabolognani/libvirt,eskultety/libvirt,andreabolognani/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,andreabolognani/libvirt,taget/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,libvirt/libvirt,rlaager/libvirt,fabianfreyer/libvirt,agx/libvirt,agx/libvirt,jfehlig/libvirt,zippy2/libvirt,VenkatDatta/libvirt,datto/libvirt,agx/libvirt,nertpinx/libvirt,nertpinx/libvirt,agx/libvirt,datto/libvirt,libvirt/libvirt,crobinso/libvirt,datto/libvirt