better template-loader error handling

Author: yyx990803

lib/template-loader.js

@@ -27,18 +27,18 @@ module.exports = function (content) {
   }
 
   if (!cons[opt.engine]) {
-    throw new Error(
+    return callback(new Error(
       'Template engine \'' + opt.engine + '\' ' +
       'isn\'t available in Consolidate.js'
-    )
+    ))
   }
 
   // for relative includes
   opt.filename = this.resourcePath
 
   cons[opt.engine].render(content, opt, function (err, html) {
     if (err) {
-      throw err
+      return callback(err)
     }
     exportContent(html)
   })