Reorder the printing of PV lines vs. statistics

It is in fact okay to print the PV after the search is stopped,
as long as we are not in multi-PV mode. Only multi-PV mode is
known to cause bogus "M0 upperbound" scores when interrupted.

Consequently, we can check for the opportunity to print the PVs
*before* checking for the need to print the nodes/time/nps statistics.
If PVs have been printed, there is no need to print the terser
"info nodes" line, since all that info is already included along
the PVs.

Added comments to that effect.

No functional change