Fix exception trying to update all translation files if the directory is empty
Escape key now prefers to cancel popups by default

That is, Escape is now checked in options -> keyboard shortcuts -> advanced
on new profiles.
Don't fallback to UTF-8 when encoding scripts

Don't know what I was thinking
[AviSynth+] Autoload plugins on environment creation

This could be needed for creating the display clip (high bit depth
options, vpy hack).
Make syntax highlighting mandatory

The info obtained from parsing the script is too useful to disregard
it, and actually some features already rely on it (therefore they
didn't work / malfunction if highlighting was disabled).
Don't release a video frame before reading its data
 Catch exceptions on GetFrame

Two reasons:
- Show uncatched filter exceptions with the same dialog as catched ones
- Avoid exceptions on exit