fix: skip empty local-repository.tmpl in nodeset

When a pkgdir has no valid repodata, Yum.pm creates an empty
local-repository.tmpl file. Template.pm then reads it and generates
an empty yum repo config block in the kickstart. Adding a -s check
skips empty template files instead of silently including them.

Revives the fix from PR #4769 which was closed without merging.

Fixes #3572

xCAT-server/lib/perl/xCAT/Template.pm

@@ -312,7 +312,7 @@ sub subvars {
                         $source .= "repo --name=pkg$c --baseurl=http://#TABLE:noderes:\$NODE:nfsserver#$httpportsuffix/$pkgdir\n"; #for rhels5.9
                     }
                     my $distrepofile="/install/postscripts/repos/$pkgdir/local-repository.tmpl";
-                    if( -f "$distrepofile"){
+                    if( -f "$distrepofile" and -s "$distrepofile"){
                         my $repofd;
                         my $repo_in_post;
                         local $/=undef;