SAX: avoid integer truncation when reporting column and line

We ported the internal implementation to qsizetype, but the public API
of QXmlLocator still reports the column and line as int.

To avoid integer truncation when reporting results, explicitly check
if the reported value is larger than INT_MAX and report -1 if it is.
This is in line with the documentation, which explicitly states that -1
is returned when no column/line number is available.

Task-number: QTBUG-149566
Pick-to: 6.12 6.12.0 6.11 6.11.3 6.8 6.5
Change-Id: I277ab4ed390d63348d426619a7c01a079d2a057f
Reviewed-by: Marc Mutz <marc.mutz@qt.io>