-Fix bug where makedhcp -a before mac table exists would result in an error

git-svn-id: https://svn.code.sf.net/p/xcat/code/xcat-core/trunk@1974 8638fb3e-16cb-4fca-ae20-7b5d299a9bcd

xCAT-server/lib/xcat/plugins/dhcp.pm

@@ -424,7 +424,11 @@ sub process_request
         {
             $req->{node} = [];
             my $mactab  = xCAT::Table->new('mac');
-            my @entries = ($mactab->getAllNodeAttribs([qw(mac)]));
+
+            my @entries=();
+            if ($mactab) {
+                @entries = ($mactab->getAllNodeAttribs([qw(mac)]));
+            }
             foreach (@entries)
             {
                 push @{$req->{node}}, $_->{node};