Accurate nps

Since Shredder GUI compatibility improvements, the engine doesn't print any PV lines after the search gets stopped. But in single-PV mode, it is in fact okay to print it. Only multi-PV mode is known to cause bogus "M0 upperbound" scores when interrupted. So the patch relaxes the condition a bit.

Consequently, we can check for the opportunity to print the PV lines *before* checking for the need to print the nodes/time/nps statistics alone. 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.

No functional change