Fixed error handling

Author: micahbule

lib/pdf.js

@@ -121,7 +121,7 @@ PDF.prototype.exec = function PdfExec (callback) {
     // Ignore if code has a value of 0 since that means PhantomJS has executed and exited successfully.
     // Also, as per your script and standards, having a code value of 1 means one can always assume that
     // an error occured.
-    if ((typeof code !== 'undefined' && code !== null) && code !== 0) {
+    if (((typeof code !== 'undefined' && code !== null) && code !== 0) || err) {
       var error = null
 
       if (err) {
@@ -134,7 +134,7 @@ PDF.prototype.exec = function PdfExec (callback) {
 
       // Append anything caught from the stderr
       var postfix = stderr.length ? '\n' + Buffer.concat(stderr).toString() : ''
-      if (postfix) err.message += postfix
+      if (postfix) error.message += postfix
 
       return callback(error)
     }