Misc ImDebugger improvements

[quirkylemon]

Changes

1. add the option to change MemCheck condition
2. draw zeros with a darker color in the memory viewer
3. fix a potential issue with a char array that is too small(?) in DrawMediaDecodersView.

When reverse engineering it can be helpful for zeros to be drawn with a darker color so you can visually see the structure of data in ram.
The new color was basically just a random choice so feel free to change it.

I only found the small char array because of a compiler warning so it is very possible that nothing bad actually happens.

[anr2me]

Is it more convenient to looked at zeroes with different color? since those zero byte could be a part of 16-bit or larger value.
Making it optional/switchable could be better.

[quirkylemon]

Yeah that's fair.
It's helpful for me to see zeros with a different color, so I'll add a toggle

[hrydgard]

Seems fine to me. I guess we could add more general value color schemes, but this is ok as-is.

Why left as draft?

[hrydgard]

Ping @quirkylemon

[quirkylemon]

sorry I was busy, I added a toggle just in case this isn't a universally helpful feature.
Also I Genuinely don't remember why I set this as a draft.