UI: Remove unnecessary vertices for preview

This change reduces the number of triangles drawn using a TRISTRIP while
still producing the same shapes for parts of the preview.

UI/window-basic-main.cpp

@@ -1452,9 +1452,8 @@ void OBSBasic::InitPrimitives()
 	gs_render_start(true);
 	gs_vertex2f(0.0f, 0.0f);
 	gs_vertex2f(0.0f, 1.0f);
-	gs_vertex2f(1.0f, 1.0f);
 	gs_vertex2f(1.0f, 0.0f);
-	gs_vertex2f(0.0f, 0.0f);
+	gs_vertex2f(1.0f, 1.0f);
 	box = gs_render_save();
 
 	gs_render_start(true);