Fix detection of invalid spaces in prolog

[gnodet]

No description provided.

[cstamas]

So this will now make XML with newline as first line always (and consistently) fail on all plaf

[gnodet]

So this will now make XML with newline as first line always (and consistently) fail on all plaf

Yes. When the xmldecl <?xml ...?> is present, it has to be at the very beginning of the file and no whitespace is allowed before. The problem is that a single whitespace could be silently discarded and it was thus failing on windows when using \r\n as the line separator because of the length of 2.