Fix broken non-Unicode MSW build

Add a missing parenthesis in a non-Unicode StartDoc() definition which
was forgotten in 948ddc6e0f (Eliminate -Wcast-qual warnings with GCC and
Clang, 2020-02-02).

Closes https://github.com/wxWidgets/wxWidgets/pull/1795

include/wx/msw/winundef.h

@@ -268,7 +268,7 @@
    #else
    inline int StartDoc(HDC h, CONST DOCINFOA* info)
    {
-      return StartDocA(h, const_cast<DOCINFOA*>(info);
+      return StartDocA(h, const_cast<DOCINFOA*>(info));
    }
    #endif
 #endif