update MD_ArenaDefault current pointer in MD_ArenaDefaultPush after allocating new arena

[chitatof]

I'm not familiar with this codebase, I was just looking at the arena implementation, so excuse me if this is not correct, but I believe it's intended that the "current" pointer is updated after adding a new arena to the linked list, which would be congruent with MD_ArenaDefaultPopTo behaviour.

[jagt]

I'm having exactly the same confusion. I assume with this change it would be the correct behavior. The default reserve size is 64mb that's large enough that the issue don't usually occur.

I took a look at raddebugger's arena impl and it's similar to this, there's indeed a line matching this change that moves the current pointer.

See https://github.com/EpicGamesExt/raddebugger/blob/aa42d12d0fe58409d52cbc950cb5e44f3a668e29/src/base/base_arena.c#L130

[KobeDB]

I also ran into this bug while doing some allocation-heavy workloads with this arena implementation. Applying chitatof's fix solved it for me!