output autosave, warning sign.

[Christa Noel]

dear all,
when i input the false file address, corona should be immediately warn me that the file address i entered is cannot be found when i hit the render button.
it is needed when some users unconsciously get their special autosave folder moved/deleted.
and it will help too because sometimes i need to work some scenes on my another computer / laptop.


thanx :-D

[Ondra]

implemented

[Christa Noel]

thanx! :-D