Was sent a sample map where the texture scale was such that the
CalcSurfaceExtents mins/maxs were calculated incorrectly because of the
use of 999999 not being large enough magnitude, leading to a crash later
(maxs-mins was negative).
git-svn-id: svn://svn.code.sf.net/p/quakespasm/code/trunk/quakespasm@1671 af15c1b1-3010-417e-b628-4374ebc0bcbd