Log mutex locked twice (leading to crash)

[alxbilger]

I encountered a situation where my code emitted a dmsg_warning. It triggers a Qt event to react, and change the component icon. However, something went wrong in the Qt side and a Qt error was emitted. Since we listen to Qt errors, it also emits a msg_*.
Therefore, a msg_* is called inside a dmsg_warning call. The problem is that a mutex protects each call when entering the message functions (PUBLIC_API_ENTRY_POINT_MUTEX). And if a mutex is locked twice in the same thread, it crashes.
To solve this situation, a std::recursive_mutex would help. But I think there is a design problem in the first place. To be discussed...

[hugtalbot]

Maybe @damienmarchal could help on this one