Assume source maps exist in node-loader

packages/node-loader/lib/index.js

@@ -63,17 +63,16 @@ export function createLoader(options) {
     if (url.protocol === 'file:' && regex.test(url.pathname)) {
       const value = await fs.readFile(url)
       const file = await process(new VFile({value, path: url}))
-      let source = String(file)
-      /* c8 ignore start -- not sure how to test this. */
-      if (file.map) {
-        source +=
+
+      return {
+        format: 'module',
+        shortCircuit: true,
+        source:
+          String(file) +
           '\n//# sourceMappingURL=data:application/json;base64,' +
           Buffer.from(JSON.stringify(file.map)).toString('base64') +
           '\n'
       }
-      /* c8 ignore stop */
-
-      return {format: 'module', shortCircuit: true, source}
     }
 
     return nextLoad(href, context)