only insert export initialisers if there are any

src/Statement.js

@@ -286,6 +286,7 @@ export default class Statement {
 								.map( name => `\n${bundleExports[name]} = ${name};` )
 								.join( '' );
 
+							if ( exportInitialisers ) {
 								// TODO clean this up
 								try {
 									magicString.insert( node.end, exportInitialisers );
@@ -295,6 +296,7 @@ export default class Statement {
 							}
 						}
 					}
+				}
 
 				const scope = node._scope;