[Cin] Checked in tweaked patches from Andrew - EXR, PNG, and TIFF

[Andrew Randrianasulu]

В сообщении от Wednesday 18 March 2020 18:57:25 Phyllis Smith написал(а):
> Andrew:
> 
> > Also, minor bug:
> >
> > If I render OpenEXR sequence, load it, play it,
> > and then delete main image files but NOT index *.exrs
> >  - and try to load file from "recent files" sub-menu in main menu - Cin
> > will terminate
> >
> > Easily reproduced here.  GG says OpenExr is doing a "throw" and Cinelerra
> normally does not "catch". This would be the very first "catch" in
> Cinelerra if it would be added and that is not the way gg wants to go
> unless we absolutely have to. This requires the error handling
> characteristics of the C++ runtime library.
> If you do that same thing with a TIFF sequence, it passes the error
> correctly back to Cinelerra to field instead of crash.
> 

H, sorry for such suggestion without patch - but can't be OpenEXR sequence 
file  validated before passing it into library?

Of course, on multiproces/user system  user may delete files right after they passes test of existence ....

May be just document it? :}