Fix tabgrep to not BUG on non-existant tables second attempt

git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@689 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd

xCAT-server-2.0/lib/xcat/plugins/tabutils.pm

@@ -726,6 +726,7 @@ sub tabgrep
     foreach (@tablist)
     {
         my $tab = xCAT::Table->new($_);
+        unless ($tab) { next; }
         if ($tab and $tab->getNodeAttribs($node->[0], ["node"]))
         {
             $callback->({data => [$_]});