Remove main opt

[lordofhyphens]

Been seeing an undefined "entry" error

Use of uninitialized value in subroutine entry at /mnt/fiver/slic3r/lib/Slic3r/GUI/Plater.pm line 1228.

Tracked it to the use of $main::opt{output}. Removed it and didn't see any changed behavior.

[lordofhyphens]

I think main::opt is actually supposed to reference "remember output directory" setting.

[alranel]

$main::opt{output} holds the contents of the CLI --output argument, which is used as default value for the export dialog. It's a pretty hidden feature, but I think it's there for a good reason.

Better to add // '' after it in order to turn the undef value to an empty string and suppress the warning.

[lordofhyphens]

Looks like this was fixed by @alexrj. Closing.