conf: Remove unnecessary checks in virSecurityLabelDefsParseXML
conf: Remove unnecessary checks in virSecurityLabelDefsParseXML

Failure would have occurred for @ctxt before in callers' other
virXPath calls and @def derefs.

Found by Coverity due to commit 66a508d2 using VIR_XPATH_NODE_AUTORESTORE
to access @ctxt before the if condition. The @def was noted by review.

Signed-off-by: John Ferlan <87558058f6f829e5ec976c8ef960720af4ff9c7d@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

crobinso/libvirt,jfehlig/libvirt,nertpinx/libvirt,jardasgit/libvirt,olafhering/libvirt,jardasgit/libvirt,crobinso/libvirt,andreabolognani/libvirt,zippy2/libvirt,eskultety/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,jardasgit/libvirt,eskultety/libvirt,fabianfreyer/libvirt,andreabolognani/libvirt,zippy2/libvirt,olafhering/libvirt,crobinso/libvirt,jardasgit/libvirt,nertpinx/libvirt,fabianfreyer/libvirt,libvirt/libvirt,andreabolognani/libvirt,eskultety/libvirt,olafhering/libvirt,zippy2/libvirt,libvirt/libvirt,zippy2/libvirt,libvirt/libvirt,jfehlig/libvirt,jfehlig/libvirt,andreabolognani/libvirt,andreabolognani/libvirt,jfehlig/libvirt,nertpinx/libvirt,eskultety/libvirt,eskultety/libvirt,nertpinx/libvirt,jardasgit/libvirt,fabianfreyer/libvirt,libvirt/libvirt,olafhering/libvirt,fabianfreyer/libvirt,crobinso/libvirt