Debug Mode display issues (UNIX build; sdl or x11)

[m0rb]

Howdy PinMAME maintainers!

Longtime fan, first time poster.

I've been wanting to delve into a few Pinball romhacks for the first time in almost a decade and wanted to use the debugger for a few projects.

I'm currently running into an issue with the debugger on a modern Linux distribution (Fedora 39, x86_64, Xorg)

I can start things up into debug mode just fine, and things display just fine. I'm able to go through the debugger in its initial state.

When I run the CPUs (*Sega Whitestar in this case) and try to return to the debugger view, the window stays completely black.

I can switch back to the running game just fine.

For yucks I tested out @francisdb's sdl2 branch but it seems to have the same issue.

Any pointers?