Break connection in workflow editor if necessary

client/galaxy/scripts/mvc/workflow/workflow-node.js

@@ -223,6 +223,11 @@ define(['mvc/workflow/workflow-view-node'], function( NodeView ) {
             $.each( data.data_outputs, function( i, output ) {
                 if (!nodeView.outputViews[output.name]) {
                     nodeView.addDataOutput(output);  // add data output if it does not yet exist
+                } else {
+                    // the output already exists, but the output formats may have changed.
+                    // Therefore we update the datatypes and destroy invalid connections.
+                    node.output_terminals[ output.name ].datatypes = output.extensions;
+                    node.output_terminals[ output.name ].destroyInvalidConnections();
                 }
             });
             this.tool_state = data.tool_state;

client/galaxy/scripts/mvc/workflow/workflow-terminals.js

@@ -134,7 +134,7 @@ define(['mvc/workflow/workflow-globals'], function( Globals ) {
         },
         destroyInvalidConnections: function( ) {
             _.each( this.connectors, function( connector ) {
-                connector.destroyIfInvalid();
+                connector && connector.destroyIfInvalid();
             } );
         },
         setMapOver : function( val ) {