Omit console log on undefined before upload rejections

[nickbabcock]

When beforeUpload function returns a rejected promise without a value (signifying do not upload) a undefined is logged to the console. It's merely a bit of annoyance, but I don't see the value added by logging undefined. I believe the below patch would fix this by ignoring undefined rejections

diff --git a/src/AjaxUploader.jsx b/src/AjaxUploader.jsx
index 638c90f..849d051 100644
--- a/src/AjaxUploader.jsx
+++ b/src/AjaxUploader.jsx
@@ -113,7 +113,7 @@ class AjaxUploader extends Component {
         }
         return this.post(file);
       }).catch(e => {
-        console && console.log(e); // eslint-disable-line
+        console && e !== undefined && console.log(e); // eslint-disable-line
       });
     } else if (before !== false) {
       setTimeout(() => this.post(file), 0);