Fix lazy initialization

[alalek]

http://code.opencv.org/issues/4428

[vpisarev]

👍

[FrankHeimes]

Where did the original detailed issue description http://code.opencv.org/issues/4428 go?
The domain has changed and I can't find it on https://github.com/opencv/opencv/issues.
I'd really like to learn the exact reasons why I should have to live with memory leak as long as I'm using OpenCV.
The static initialization chaos alone is no longer a reason when using C++11 and Meyers Singleton pattern.

[FrankHeimes]

@soechin: @alalek is right saying that your solution doesn't work because __initialization_mutex may be not be initialized before getInitializationMutex() is called by another static initializer.

But this should work with C++11:

Mutex& getInitializationMutex()
{
  static Mutex instance; // Initialization is thread-safe
  return instance;
}

especially if no (non-constexpr) static variables exist in global scope.