Minor fixes

[malte0811]

ece59ac: This is "nice to have" in general, and also fixes a strange SIGSEGV I have been running into when launching MC in dev.

4df082e: Before only put/remove calls were synchronized, which prevented two simultaneous modifications, but not a modification during a read. If there are performance concerns about using a "general purpose" lock/mutex here I can replace it with a ReadWriteLock.

[malte0811]

Clearly this repo and the idiots running it are not interested in external contributions, to the degree where even asking for additional justification is too much work.

[LexManos]

Whelp, called the rage quit. Anyways, as stated in the other issue. The reason this one was left alone is because it contained no justification. No discussion with anyone else. No reproduction steps. And until just recently was unverified to actually exist {none of the team had encountered it even while trying to reproduce}. Luckily one of our other community members was able to independently run into this issue on their own and actually sat down to understand and explain the issue.

Just for the record, malte has a history of these 'Just do what I say' without explanation PRs, and a history of throwing a fit if we try and verify or get any more information out of him. So my personal approach is to ignore until a 3rd party can verify/deal with it. (Which is why this PR has no response, even tho I've seen it)

You're more then welcome to submit issues/fixes if you're willing to discuss and back them up.