maint: avoid unbalanced {} across vbox #ifdef

maint: avoid unbalanced {} across vbox #ifdef

Emacs is fairly good about navigating across function and scope
boundaries, provided that the code has balanced {}.  The vbox
code, however, violated that premise, by splitting 'if () {'
across several #ifdef branches, but sharing the '} else {...}'
outside of the branches.  The extra lines of code is worth my
sanity, in a function that is already a horrendous 1100+ lines
long.

* src/vbox/vbox_tmpl.c (vboxDomainGetXMLDesc) Duplicate code
rather than trying to share else branch across #ifdef.

Signed-off-by: Eric Blake <eblake@redhat.com>