fix empty array error

src/main.v

@@ -133,8 +133,10 @@ fn get_ppu() !f64 {
 	mut people := sql db {
 		select from Person where status == 3
 	}!
+	if people.len == 0 {
+		return 0
+	}
 	people.sort(a.order_time < b.order_time)
-
 	time_range := people.last().order_time - people.first().order_time
 	return people.len / time_range.hours()
 }