Fix harmless warning about using wxCONTROL_CHECKED in ternary operator.

Add wxCONTROL_NONE which is just a symbolic name for 0 and use it in the code
to avoid g++ 4.8 warnings about mixing enum and int in conditional expression.

Closes #16242.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@76484 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/renderer.h

@@ -52,6 +52,7 @@ class WXDLLIMPEXP_FWD_CORE wxWindow;
 // control state flags used in wxRenderer and wxColourScheme
 enum
 {
+    wxCONTROL_NONE       = 0x00000000,  // absence of any other flags
     wxCONTROL_DISABLED   = 0x00000001,  // control is disabled
     wxCONTROL_FOCUSED    = 0x00000002,  // currently has keyboard focus
     wxCONTROL_PRESSED    = 0x00000004,  // (button) is pressed