Fix/remove some bad std::moves

[tfc]

Motivation

While being at it, I grepped through the source to identify more positions with bad std::move usage.

I particularly fixed 2 types of moves (grouped in two different commits):

• bla = *std::move(some_optional); - this moves an optional and then copies its content. The dereference operator must go into the move
• return std::move(some_stack_var) - these moves are superfluous as they would be moved to the caller anyway, but they even forbid named return value optimization (NRVO) where it would otherwise be applicable.

Context

Priorities

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[Ericson2314]

I was preferring the first one because I thought std::move would set the std::optional back to std::nullopt, but I guess it does not.

[tfc]

I was preferring the first one because I thought std::move would set the std::optional back to std::nullopt, but I guess it does not.

No, there is no guarantee on that. It would be nice of the implementer of the move-constructor/assignment-operator to implement it this way, but it is not safe to assume anything on the state of the moved-from object.