Default-init atomics in TaskManager::Impl

std::atomic<bool> does not value-initialise the boolean.
This caused windows tests to use way too much CPU and fail.

Differential Revision: https://code.wildfiregames.com/D4089
This was SVN commit r25687.

source/ps/TaskManager.cpp

@@ -141,8 +141,8 @@ protected:
 	// Back reference (keep this first).
 	TaskManager& m_TaskManager;
 
-	std::atomic<bool> m_HasWork;
-	std::atomic<bool> m_HasLowPriorityWork;
+	std::atomic<bool> m_HasWork = false;
+	std::atomic<bool> m_HasLowPriorityWork = false;
 	std::mutex m_GlobalMutex;
 	std::mutex m_GlobalLowPriorityMutex;
 	std::deque<QueueItem> m_GlobalQueue;