New Draw.io diagrams can't load images if username contains emoji character #1993

Describe the bug
I don't even know if this is necessarily worth the time in fixing, but if a user has an emoji in their username and creates a draw.io diagram - the image is generated on the filesystem but BookStack gets HTTP 500 error trying to load it

Steps To Reproduce
Steps to reproduce the behavior:

1. Create a new user with an emoji character in their name
2. Create a draw.io diagram within a page
3. Save the diagram
4. See error in that image does not display & web console error 500

Expected behavior
I expect that upon saving the png generated of the diagram is displayed on my finished page

Screenshots

Your Configuration (please complete the following information):

• Tested on demo site in screenshot above

Additional context
I haven't tested with many emojis, it's possible some of them work.