Common: Enforce explicit handle validation

Some invalid handle values are -1 or INVALID_HANDLE_VALUE, hence our
handle template has a specific invalid handle value parameter we should
always test against. Time and again, I find my code simply comparing
handle against zero.

Signed-off-by: Simon Rozman <simon@rozman.si>

include/stdex/stream.hpp

@@ -2383,6 +2383,9 @@ namespace stdex
 			socket(_In_ const socket& other);
 			socket& operator =(_In_ const socket& other);
 
+			// Force use of valid() method when testing handle.
+			operator bool() const;
+
 		public:
 			socket(_Inout_ socket&& other) noexcept : m_h(other.m_h)
 			{

include/stdex/system.hpp

@@ -200,6 +200,10 @@ namespace stdex
 		///
 		operator T() const noexcept { return m_h; }
 
+	private:
+		// Force use of valid() method when testing handle.
+		operator bool() const;
+
 	protected:
 		T m_h;
 	};