Fix unhandled error when obj or mtl is missing

lib/readLines.js

@@ -2,6 +2,7 @@
 const fsExtra = require("fs-extra");
 const Promise = require("bluebird");
 const readline = require("readline");
+const events = require("events");
 
 module.exports = readLines;
 
@@ -15,8 +16,9 @@ module.exports = readLines;
  * @private
  */
 function readLines(path, callback) {
-  return new Promise(function (resolve, reject) {
   const stream = fsExtra.createReadStream(path);
+  return events.once(stream, "open").then(function () {
+    return new Promise(function (resolve, reject) {
       stream.on("error", reject);
       stream.on("end", resolve);
 
@@ -34,4 +36,5 @@ function readLines(path, callback) {
 
       lineReader.on("line", callbackWrapper);
     });
+  });
 }