QLocal8Bit::convertToUnicode[win]: Fix order of growth and saturate

The order was wrong so we could have ended up saturating a 0
before we grew to 1.
Since this has never been in a release it is of no concern, and it was
already an edge-case anyway.

Amends 1090d5dd4ae5be898d4566314eda43b0283709d9

Pick-to: 6.7 6.6 6.5
Change-Id: I4b70f9018c3049697495a58313af148f8366c8bb
Reviewed-by: Marc Mutz <marc.mutz@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

src/corelib/text/qstringconverter.cpp

@@ -1365,10 +1365,10 @@ QString QLocal8Bit::convertToUnicode_sys(QByteArrayView in, quint32 codePage,
     // encounter an error
     int nextIn = qt_saturate<int>(mblen);
     while (mblen > 0) {
-        const int nextOut = qt_saturate<int>(outlen);
         std::tie(out, outlen) = growOut(1); // Need space for at least one character
         if (!out)
             return {};
+        const int nextOut = qt_saturate<int>(outlen);
         len = MultiByteToWideChar(codePage, MB_ERR_INVALID_CHARS, mb, nextIn, out, nextOut);
         if (len) {
             mb += nextIn;