racket/gui win32: fix measurement of message% content

Strip away "&" before measuring.

original commit: 58e24e18a27fee2b6b487f5163c2eda48e347546

pkgs/gui-pkgs/gui-lib/mred/private/wx/win32/message.rkt

@@ -88,7 +88,7 @@
 
     (if (symbol? label)
         (set-size #f #f 32 32)
-        (auto-size font label 0 0 0 0))
+        (auto-size font (strip-& label) 0 0 0 0))
 
     (define/public (set-preferred-size) #f)
 

pkgs/gui-pkgs/gui-lib/mred/private/wx/win32/utils.rkt

@@ -47,6 +47,7 @@
               SelectObject
               WideCharToMultiByte
 	      GetDeviceCaps
+	      strip-&
 	      ->screen
 	      ->normal))
 
@@ -163,6 +164,13 @@
                                             -> _int))
 ;; ----------------------------------------
 
+(define (strip-& s)
+  (if (string? s)
+      (regexp-replace* #rx"&(.)" s "\\1")
+      s))
+
+;; ----------------------------------------
+
 (define-gdi32 GetDeviceCaps (_wfun _HDC _int -> _int))
 
 (define screen-dpi