fopen() Exception when exporting to pdf document #2746

Describe the bug
After upgrading V21.04.4 I can't export to PDF:

Steps To Reproduce
Steps to reproduce the behavior:

1. Go to a page or chapter

2. Click on export, than on PDF file

3. See error
   

Your Configuration (please complete the following information):

• Exact BookStack Version (Found in settings): V21.04.4
• PHP Version: 7.4.16
• Hosting Method (Nginx/Apache/Docker): Windows 10 / IIS

Additional context
The referenced directory does not exists. I believe c:\BookStack\app\vendor\.... should be c:\BookStack\vendor\.... (without \app).
Just for testing, after manually creating the directory, the export does work.