potential unreleased locks

[joprice]

I noticed that the use of locks in the QueueManager, especially the one that throws, could end up holding onto the lock too long:

SwiftAudioEx/Sources/SwiftAudioEx/QueueManager.swift

Lines 20 to 32 in 4276703

	fileprivate func synchronizeThrows<T>(action: () throws -> T) throws -> T {
	recursiveLock.lock()
	let result = try action()
	recursiveLock.unlock()
	return result
	}
	fileprivate func synchronize <T>(action: () -> T) -> T {
	recursiveLock.lock()
	let result = action()
	recursiveLock.unlock()
	return result
	}

. I'm not a swift expert, but moving unlock into a defer block should guarantee that the lock is released on exiting. I haven't repro'd this, but I would think any failable function being passed to synchronizeThrows would cause later operations to hang.