include: Add cast to avoid a compiler warning on MSVC.

Wine-Bug: https://bugs.winehq.org/show_bug.cgi?id=46991
Signed-off-by: Alexandre Julliard <julliard@winehq.org>

include/wine/debug.h

@@ -290,7 +290,7 @@ static inline const char *wine_dbgstr_wn( const WCHAR *str, int n )
                 *dst++ = hex[(c >> 4) & 0x0f];
                 *dst++ = hex[c & 0x0f];
             }
-            else *dst++ = c;
+            else *dst++ = (char)c;
         }
     }
     *dst++ = '"';