Fixed bug in `removeTilesOlderThan` #624

Job	Run time
Run Tests	2m 37s
Analyse Code	1m 35s
Score Package	2m 13s
Build Tile Server (Windows)	48s
Build Demo App (Windows)	5m 19s
Build Tile Server (Linux/Ubuntu)	21s
Build Demo App (Android)	4m 56s
	17m 49s

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