Address the issue coalescing two records together when TrimLeadingSpace
is set to true.

The input

        a,b,
        c,d,e

Would result with a singled a,b,c,d,e record.
With TrailingComma set to true it should give two records.
With TrailingComma set to false it should be an error.

Fixes #2366.

R=golang-dev, go.peter.90, r
CC=golang-dev
https://golang.org/cl/5284046