the x. column prefixes in j not found when by=.EACHI #1761

library(data.table)
dt = data.table(a=1L)
dt[dt, .(xa=x.a, ia=i.a), on="a"]
#   xa ia
#1:  1  1
dt[dt, .(xa=x.a, ia=i.a), .EACHI, on="a"]
#Error in `[.data.table`(dt, dt, .(xa = x.a, ia = i.a), .EACHI, on = "a") :
#  object 'x.a' not found