ASN UTCTime uses two characters to encode a year (YY). When converting it
into QDate, it's quite naive to just add 2000. According to RFC 2459,
these YY represent dates in the range [1950, 2049].
This patch also introduces a helper function doing the checked conversion
from a string to int (to be reused in the following-up patches).
Task-number: QTBUG-61934
Change-Id: I3f6f471d24e8357b83b2f5973023b2b842751389
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: Timur Pocheptsov <timur.pocheptsov@qt.io>
07c0e0fdcf