MFV: zstd: FIO_addFInfo: Fully initialize output 'total' struct

Silence a Coverity warning about 'windowSize' being uninitialized.
(Yes, nothing that calls this routine actually uses the windowSize
value. Still, appeasing Coverity is pretty harmless in this case.)

Reported by: Coverity
Reviewed by: Yann Collet
Obtained from: zstd 606374269cf3485972c90b993fbb84dc20da032f
Sponsored by: Dell EMC Isilon