libobs-d3d11: Allow multiple display captures of same monitor

This commit fixes a bug that occurs on Windows 8+ when two or more
"Display Capture" sources are active that are configured to capture the
same monitor.  Only one display capture would show, while all subsequent
display captures would display nothing.

Closes jp9000/obs-studio#1142

libobs-d3d11/d3d11-subsystem.hpp

@@ -561,6 +561,8 @@ struct gs_duplicator : gs_obj {
 	ComPtr<IDXGIOutputDuplication> duplicator;
 	gs_texture_2d *texture;
 	int idx;
+	long refs;
+	bool updated;
 
 	void Start();