Change timestamp: Value changes to floating point value

[larsen]

Steps to reproduce:

- Have image with date "30.08.2015"
- Change timestamp, enter "1234" manually
Date would be changed to "15.01.2019"

- Click on "up" arrow
Value changes to "1.235" and date to "31.08.2015" (time is not changed)
--> Value should change to "1235" without the point.

Using XnView 2.34 on Win 7, SP1, German