Skip genes that are listed in Compara but aren't in the relevant core...

Skip genes that are listed in Compara but aren't in the relevant core databases. Shouldn't be necessary in production runs but makes testing with previous Compara versions easier.

misc-scripts/xref_projection/project_display_xrefs.pl

@@ -188,12 +188,16 @@ foreach my $to_species (@to_multi) {
 
     my $from_gene = $from_ga->fetch_by_stable_id($from_stable_id);
 
+    next if (!$from_gene);
+
     my @to_genes = @{$homologies->{$from_stable_id}};
     my $i = 1;
     foreach my $to_stable_id (@to_genes) {
 
       my $to_gene = $to_ga->fetch_by_stable_id($to_stable_id);
 
+      next if (!$to_gene);
+
       project_display_names($to_ga, $to_dbea, $from_gene, $to_gene, $i, scalar(@to_genes), %db_to_type) if ($names);
 
       project_go_terms($to_ga, $to_dbea, $ma, $from_gene, $to_gene) if ($go_terms);