Fix an uninitialized variable causing (harmless) OpenGL errors. Resolves issue #1434.

src/modules/graphics/opengl/FenceSync.h

@@ -38,7 +38,7 @@ class FenceSync
 {
 public:
 
-	FenceSync() {}
+	FenceSync() : sync(0) {}
 	~FenceSync();
 
 	bool fence();