Update: Invoke callback with error or result, not both, when reading contents (#259)

Author: erikkemperman

lib/src/read-contents/index.js

@@ -39,7 +39,10 @@ function readContents(optResolver) {
     // This is invoked by the various readXxx modules when they've finished
     // reading the contents.
     function onRead(readErr) {
-      callback(readErr, file);
+      if (readErr) {
+        return callback(readErr);
+      }
+      return callback(null, file);
     }
   }