Output PV if last iteration does not complete

Output PV if last iteration does not complete

Instead of outputting "info nodes ... time ..." when the last
iteration is interrupted, simply call UCI::pv() to output the PV.

I thought about calling UCI:pv() with bounds -VALUE_INFINITE, VALUE_INFINITE
to avoid "lowerbound" or "upperbound" appearing in it, but I'm not sure that
would be any better.

This patch fixes rare inconsistencies between the first move of
the last PV output and the bestmove played. It also makes sure
that all the latest statistics are sent to the GUI (not only nodes
and time but also nps, tbhits, hashfull).

No functional change.