Replace an incorrect math.max() by math.min() in tileclass

Summary: Patch by smiley fixing rP21026

Test Plan:
Check that is the correct fix.
Measure how badly it affected performance.

Reviewers: O14 Maps, elexis, Stan

Reviewed By: O14 Maps, elexis

Subscribers: smiley

Trac Tickets: #4992

Differential Revision: https://code.wildfiregames.com/D2010