\r newlines are squashed in a single-column file

[st-pasha]

> fread("A\r1\r\r\r2\r")
   A
1: 1
2: 2
> fread("A\n1\n\n\n2\n")
    A
1:  1
2: NA
3: NA
4:  2

Both examples should produce identical results (4-row DT), however in the first case all \rs are squashed and as a result NA values in the file disappear.