Fix QP favg stat.

src/qp.c

@@ -565,7 +565,7 @@ qp_stats(const struct qp_y * const restrict y,
 	if (fanout > stats->fmax)
 		stats->fmax = fanout;
 	stats->favg +=
-		(fanout - stats->favg) / ((stats->nodes - stats->terms) + 1.);
+		(fanout - stats->favg) / ((stats->nodes - stats->leaves));
 
 	for (int i = 0; i < popcount(y->bitmap); i++)
 		qp_stats(y->branch[i], strings, stats, depth);