Fail to read multiple-line string with multiple tasks

[huangyxi]

CSV.read failed when CSV files contain multiple-line strings with multiple tasks.

Reproduction

Threads.nthreads() # 240
using DataFrames
using CSV

n = 4000 # change to larger number if unable to reproduce
text = "123
abc" # multiple-line string
a = DataFrame(id=1:n, text=fill(text, n))
CSV.write("test.csv", a)
b = CSV.read("test.csv", DataFrame) # Error
# CSV.read("test.csv", DataFrame, ntasks=1) is OK