Incorrect long to short filename conversions

[DrDos0016]

The web version of Zeta handles converting long filenames to the 8.3 format used by DOS, but the method it uses is not always correct.

Currently, the code uses the first 6 (or fewer) characters and appends the ~# suffix, however the first six characters should be the first six characters without spaces.

https://museumofzzt.com/file/play/the%20search%20for%20the%20lost%20brother%20series/ is an example in the wild.

"Lost Brother DEMO.zzt" is the full filename.
Zeta converts it to "LOST B1", which is what is shown in the world menu and fails to load.
DOSBox converts it to "LOSTBR1" which matches the ZZT file's internal world name and loads correctly.