Date fallback in (imported) placements not working

[mbergen]

Describe the bug
When prizepool import fetches a match without a date, the corresponding placement object also has the default date set, instead of falling back to the tournament enddate

To Reproduce
Steps to reproduce the behavior:
https://liquipedia.net/dota2/Merlini/Results
https://liquipedia.net/dota2/Kiev_Major/2017/North_America/Open_Qualifier/1 placement "Vegetables Esports Club"

Expected behavior
When the match does not have a date set, the placement date should fall back to tournament enddate.