Compilation fix for ANSI build after r61898.

wxWX2MBbuf is just char* if wxUSE_UNICODE==0 and so doesn't have a length()
method, use wxString::length() in wxFile::Write() instead.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61953 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/file.cpp

@@ -312,7 +312,12 @@ bool wxFile::Write(const wxString& s, const wxMBConv& conv)
   if ( !buf )
       return false;
 
+#if wxUSE_UNICODE
   const size_t size = buf.length();
+#else
+  const size_t size = s.length();
+#endif
+
   return Write(buf, size) == size;
 }