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;
 
@@ -15,23 +16,25 @@ module.exports = readLines;
  * @private
  */
 function readLines(path, callback) {
-  return new Promise(function (resolve, reject) {
+  const stream = fsExtra.createReadStream(path);
-    const stream = fsExtra.createReadStream(path);
+  return events.once(stream, "open").then(function () {
-    stream.on("error", reject);
+    return new Promise(function (resolve, reject) {
-    stream.on("end", resolve);
+      stream.on("error", reject);
+      stream.on("end", resolve);
 
-    const lineReader = readline.createInterface({
+      const lineReader = readline.createInterface({
-      input: stream,
+        input: stream,
+      });
+
+      const callbackWrapper = function (line) {
+        try {
+          callback(line);
+        } catch (error) {
+          reject(error);
+        }
+      };
+
+      lineReader.on("line", callbackWrapper);
     });
-
-    const callbackWrapper = function (line) {
-      try {
-        callback(line);
-      } catch (error) {
-        reject(error);
-      }
-    };
-
-    lineReader.on("line", callbackWrapper);
   });
 }