Do not add extra space after left delim in empty line

[Masquue]

s:CommentLines currently add an extra space after left delim regardless if the line is empty.

This causes the following code (cursor position represented as |):

{
|
}

if using command V\cc, to be formatted as (space represented as _):

{
//_
}

This patch removes this extra trailing space on empty lines in s:CommentLines.

[Masquue]

Closing as there is already an option 'NERDTrimTrailingWhitespace' which does this.

But the doc is in correct as it says

'NERDTrimTrailingWhitespace' Specifies if trailing whitespace should be deleted when uncommenting

Trailing whitespaces are also trimmed when commenting.