nir/vars_to_ssa: Handle UNDEF_NODE in more places
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110832 Fixes: 911ea2c6 "nir/vars_to_ssa: Use a non-null UNDEF_NODE pointer"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110832 Fixes: 911ea2c6 "nir/vars_to_ssa: Use a non-null UNDEF_NODE pointer"