user32: Don't crash for unknown button styles

[André Hentschel]

got that case with an MFC application which had a 3state radiobutton with buttonstyle 15(decimal)
with this fix everything is fine as the painting of the button is handled elsewhere, without that fix it crashes as it reads bad data behind the array.

---
 dlls/user32/button.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/dlls/user32/button.c b/dlls/user32/button.c
index 54d54dc..4f629f0 100644
--- a/dlls/user32/button.c
+++ b/dlls/user32/button.c
@@ -197,7 +197,7 @@ static inline UINT get_button_type( LONG window_style )
 /* paint a button of any type */
 static inline void paint_button( HWND hwnd, LONG style, UINT action )
 {
-    if (btnPaintFunc[style] && IsWindowVisible(hwnd))
+    if (style <= MAX_BTN_TYPE && btnPaintFunc[style] && IsWindowVisible(hwnd))
     {
         HDC hdc = GetDC( hwnd );
         btnPaintFunc[style]( hwnd, hdc, action );
-- 

Best Regards, André Hentschel