Print/merge document has awkward filename if activity subject uses non-english letters
For example if the activity subject is entered in russian the filename now looks like:
4hGbFjlOwHfeQx47ozW73rjd7qXWsDCm1BbViImz4fCo37Nu8577jElZKCx9swWWBnjEKX1sGMdMeaOKj6RjlRGZ9kBpgaAdME7LPEFWgV1tJQ01rhiYksubVULNej2OBxuaytIYl6WHe83wtEhb9tMTzmK7HkG0tcCDaqz69UI6rfJdlRZeKRkcU2xckpqNOuKtnXct.pdf
In french and similar it's not too bad but accents get replaced by _, e.g. reçu becomes re_u.pdf
It's from the use of munge() in https://github.com/civicrm/civicrm-core/pull/21006. It needs something to escape malicious input or avoid invalid filenames, but munge() might not be the best choice here.
That was just merged yesterday so only affects master.
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