TupleBatch: fix mod error in partitionInto
TupleBatch: fix mod error in partitionInto

First, do the mod. Second, be aware that mod can be negative.

Signed-off-by: Daniel Halperin <1a02732a15f637c31107256cbee5819e36aa7c67@cs.washington.edu>

jamesmarva/myria,bsalimi/myria,jamesmarva/myria,uwescience/myria,uwescience/myria,jamesmarva/myria,bsalimi/myria,bsalimi/myria,uwescience/myria