Defer: Allow to cancel the callback before going out of scope

lib/base/defer.hpp

@@ -30,13 +30,21 @@ public:
 	inline
 	~Defer()
 	{
-		try {
+		if (m_Func) {
-			m_Func();
+			try {
-		} catch (...) {
+				m_Func();
-			// https://stackoverflow.com/questions/130117/throwing-exceptions-out-of-a-destructor
+			} catch (...) {
+				// https://stackoverflow.com/questions/130117/throwing-exceptions-out-of-a-destructor
+			}
 		}
 	}
 
+	inline
+	void Cancel()
+	{
+		m_Func = nullptr;
+	}
+
 private:
 	std::function<void()> m_Func;
 };