Fix gcc warning reported by Imarok after rP23690
Introduced in rP23690.
Gcc gives warning about missing parenthesis so this patch is adding them, not changing result of expression.
Fix proposed by Imarok in P206 after report on irc http://irclogs.wildfiregames.com/2020-05/2020-05-22-QuakeNet-%230ad-dev.log.
Differential Revision: https://code.wildfiregames.com/D2762
Reviewed by: elexis