Fix resize freeze on full-width chars in Terminal history

In the Terminal data model every full width character occupies two cells
in the data buffers. The second cell of such characters is not drawn and
used mainly to differentiate between full width and half width
characters.
Proposed fix zeroes the attributes of the second cell in the
HistoryBuffer::GetTerminalLineAt() that prevents the potential endless
loops in the BasicTerminalBuffer::_ResizeRedraw(). Those loops were
result of the random attributes in full width character's second cells.