Bug on subset of 1-row data.table when expr returns a named logical vector

```r
require(data.table)
options(datatable.auto.index=FALSE)
dt <- data.table(x=1, y="a")
val <- c(foo=1L)
dt[x == val] # returns wrong result
# Empty data.table (0 rows) of 2 cols: x,y

dt[x == unname(val)]
#    x y
# 1: 1 a
```