Fix CollapsibleWidget scissors

[fgnm]

Hi,
I've noticed that when a CollapsibleWidget is placed in a scroll pane and it's partially visible scissors doesn't get applied because ScissorStack.pushScissors fails, this produce bugs like that:

Checking Y position before rendering should fix the problem, let me know.

Thanks!

[czyzby]

Checking Y position before rendering should fix the problem, let me know.

@fgnm Have you tested it locally in your application? Since you have a reproducible example, I'd appreciate it if you tested it in your environment. You can either install the snapshot version of VisUI and pull it from Maven Local in your project, or simply copy-paste the class and use your modified version just to verify the fix. Thanks.

[fgnm]

Sure, I've already tested it before open this PR, also tried some different solutions, but this was the best I've found :)
That's how it works with the fix:

[czyzby]

OK, I misunderstood the original post.

The change seems harmless enough, but just to be sure - have you also checked if the widget is drawn properly outside of the scrollpane, and if the horizontal collapsible didn't break? Otherwise I think we can merge this as is. Thanks.

[fgnm]

I've checked the VisUI test application both with vertical and horizontal widget, no issue. I use CollapsibleWidget also in some other cases, no bug noticed too.