Bug 34617: Preserve calculated expiration dates if set to update on import whether...

Bug 34617: Preserve calculated expiration dates if set to update on import whether column included or not

To test:
1 - Setup a csv with column headers:
    surname	firstname	branchcode	categorycode	cardnumber	dateenrolled
2 - add values
    Acosta	Edna	CPL	PT	23529001000463	02/01/2013
3 - Set PT catgeory enrollement period to a specific date in the future
4 - Import the file and overwrite patrons and update dateexpiration
5 - Check Edna, note her date is not correct
6 - Apply patch
7 - Repeat
8 - Expiration date is now set as expected

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>