various tweaks & fixes

Mostly for
https://github.com/libgdx/libgdx/issues/2359
https://github.com/libgdx/libgdx/issues/2524
https://github.com/libgdx/libgdx/issues/2441
https://github.com/libgdx/libgdx/issues/2436

I'd rather not add `<?>` everywhere. It's the same as omitting it, just noisier.