buffer last line without new line end

[ChristopherHX]

This change looks large if whitespace changes are shown in diff....

This may not happen in act, but node doesn't ensure this will never happen.

e.g.
handeIO called with

line1
line2
line3
{.......................................................................................

now called again, notice no \n on the end of the buffer

.....................}
line5

this one ends with a newline again.

This change now buffers {....................................................................................... and joins it with .....................} to have a valid json line.

typeof j.msg === 'string is true as well if msg="", even if you cannot get act to log such thing by echo '' it's possible.

My Runner.Client transfers empty lines like that.