[ENSCORESW-755]. Avoid contig vs chr length test in case of circular chromosome.

When a feature is returned by a method in its coordinate system (e.g. fetch_by_dbID)
and it's on a circular chromosome and spans the origin of replication,
Mapper::add_map_coordinates aborts since it's testing the length of the contig
against the difference between chr_end and chr_start.

modules/Bio/EnsEMBL/Mapper.pm

@@ -550,7 +550,7 @@ sub add_map_coordinates {
     throw("7 arguments expected");
   }
 
-  if ( ( $contig_end - $contig_start ) != ( $chr_end - $chr_start ) ) {
+  if ( ( $chr_end > $chr_start ) and ( $contig_end - $contig_start ) != ( $chr_end - $chr_start ) ) {
     throw("Cannot deal with mis-lengthed mappings so far");
   }