SharePoint Designer 2013 Opens Blank Workflow When 'Edit Workflow' Clicked

First and foremost, you should try to clear the cache as mentioned in this article by Sagar Pardeshi.
Summary of the issue resolution given in the above article,
Clear your SharePoint Designer cache from the below location (press Windows+R from your Windows machine and paste the below links individually).
  • %USERPROFILE%\AppData\Local\Microsoft\WebsiteCache
  • %APPDATA%\Microsoft\Web Server Extensions\Cache
If the issue still persists, keep on reading.
If clearing the cache does not work for you, you need to download the latest kb update from Microsoft about SPD.
This fixed the issue for me.
Common issues you might face after installing SharePoint Designer from the above link.
  1. SharePoint Designer failed to load this workflow
  2. SharePoint Designer failed to load the workflow definition for the workflow
  3. SharePoint Designer failed to load the configuration file for the workflow
Please ensure that,
  • You have the latest version of SPD installed.
  • You have followed the above steps and cleared SPD cache.
Do feel free to post your feedback and further error (if any) so that we can try to reach a resolution stage.