Access reexports of externals safely when needed.

src/finalisers/shared/getExportBlock.js

@@ -1,22 +1,24 @@
+function wrapAccess ( id ) {
+	return ( id.originalName !== 'default' && id.module && id.module.isExternal ) ?
+		id.module.name + propertyAccess( id.originalName ) : id.name;
+}
+
 function propertyAccess ( name ) {
 	return name === 'default' ? `['default']` : `.${name}`;
 }
 
 export default function getExportBlock ( bundle, exportMode, mechanism = 'return' ) {
 	if ( exportMode === 'default' ) {
-		const defaultExportName = bundle.exports.lookup( 'default' ).name;
+		const id = bundle.exports.lookup( 'default' );
 
-		return `${mechanism} ${defaultExportName};`;
+		return `${mechanism} ${wrapAccess( id )};`;
 	}
 
 	return bundle.toExport
 		.map( name => {
 			const id = bundle.exports.lookup( name );
 
-			const reference = ( id.originalName !== 'default' && id.module && id.module.isExternal ) ?
-				id.module.name + propertyAccess( id.name ) : id.name;
-
-			return `exports${propertyAccess( name )} = ${reference};`;
+			return `exports${propertyAccess( name )} = ${wrapAccess( id )};`;
 		})
 		.join( '\n' );
 }