Log an error if getstats() returns a failure

I saw my logon.jsonl file getting cycled multiple times a day recently on Vert
and suspect this function call may have been failing.

src/sbbs3/logon.cpp

@@ -599,7 +599,10 @@ uint sbbs_t::logonstats()
 	struct tm tm, update_tm;
 
 	sys_status&=~SS_DAILY;
-	getstats(&cfg, 0, &stats);
+	if(!getstats(&cfg, 0, &stats)) {
+		errormsg(WHERE, ERR_READ, "system stats");
+		return 0;
+	}
 
 	now=time(NULL);
 	if(stats.date > now+(24L*60L*60L)) /* More than a day in the future? */