need data.table() to restore alloccol message consistency

Author: MichaelChirico

inst/tests/tests.Rraw

@@ -15883,6 +15883,7 @@ l = list(foo=list(bar=data.frame(a=1:3, b=4:6)))
 test(2074.041, setDT(l[[c('foo', 'bar')]]), error='Invalid set* operation on a recursive index L[[i]]')
 setDT(l[['foo']][['bar']])
 test(2074.042, is.data.table(l[[c('foo', 'bar')]]))
+l = list(foo=list(bar=data.table(a=1:3, b=4:6)))
 test(2074.043, l[[c('foo', 'bar')]][ , (letters) := 16:18], error='Invalid set* operation on a recursive index L[[i]]')
 options(opt)
 ## alloc.col when using 0-truelength j assigning to a subset