Call to _create_feature_fast set default ([]) to 'attributes' value so as to

eliminate the need for a specialised MiscFeature::new_fast implementation.

modules/Bio/EnsEMBL/DBSQL/MiscFeatureAdaptor.pm

@@ -513,7 +513,7 @@ sub _objs_from_sth {
                                        'slice'   => $slice,
                                        'adaptor' => $self,
                                        'dbID'    => $misc_feature_id,
-                                       'attributes' => $feat_attribs
+                                       'attributes' => $feat_attribs ||= []
                                      } );
 
       push @features, $feat;