Fix invalid request parsing.

[anton-barabanov]

Problem is in case, when buffer stops reading in the last symbol of the line. Next time it will read '\r\n' sequence and interpret it as an empty line and set _end to true.

[obiltschnig]

I don't understand what issue this is solving.

[aleks-f]

I guess what @anton-barabanov is saying is that, when readFromDevice reads \r\n only, it will interpret it as the end prematurely. But I'm not sure this fix is good and how to produce a test reproducing it.