win32: avoid continued failure when painting fails

original commit: a5c4863848279b205411aa8ce2400ff02afc3a32

collects/mred/private/wx/win32/canvas.rkt

@@ -155,6 +155,7 @@
         [(= msg WM_PAINT)
          (let* ([ps (malloc 128)]
                 [hdc (BeginPaint w ps)])
+	   (when hdc
              (if for-gl?
                  (queue-paint)
                  (if (positive? paint-suspended)
@@ -171,7 +172,7 @@
                            (DeleteObject hbrush)))
                        (unless (do-canvas-backing-flush hdc)
                          (queue-paint)))))
-           (EndPaint hdc ps))
+             (EndPaint hdc ps)))
          0]
         [(= msg WM_NCPAINT)
          (if control-border-theme

collects/mred/private/wx/win32/window.rkt

@@ -56,8 +56,6 @@
                                      -> (unless r (failed 'ClientToScreen))))
 
 (define-gdi32 CreateFontIndirectW (_wfun _LOGFONT-pointer -> _HFONT))
-(define-user32 FillRect (_wfun _HDC _RECT-pointer _HBRUSH -> (r : _int)
-                               -> (when (zero? r) (failed 'FillRect))))
 
 (define-shell32 DragAcceptFiles (_wfun _HWND _BOOL -> _void))