Fixing time check for years > 2000

Fixing the year2digit method in haem::time for years > 2000

The time check for years > 2000 was checking and amending a local variable, but the check for years > 1900 was checking the struct variable, and changing the local variable. This meant that for years > 2000, 3900 was being deducted (e.g. 2019 --> -1881).