Don't rollover daily stats (dsts.ini) if the previous date was Jan-1-1970 UTC

This date (basically 0) means either the dsts.ini file doesn't exist or there
was an issue reading it successfully (that was not detected by getstats()).

src/sbbs3/logon.cpp

@@ -616,6 +616,7 @@ uint sbbs_t::logonstats()
 		return 0;
 	}
 
+	if(stats.date != 0) {
 		now=time(NULL);
 		if(stats.date > now+(24L*60L*60L)) /* More than a day in the future? */
 			errormsg(WHERE,ERR_CHK,"Daily stats date/time stamp", (ulong)stats.date);
@@ -654,20 +655,22 @@ uint sbbs_t::logonstats()
 					continue;
 				}
 
+				dstats_fname(&cfg, i, path, sizeof path);
 				if(!fread_dstats(dsts, &stats)) {
-				errormsg(WHERE, ERR_READ, "dsts.ini", i);
+					errormsg(WHERE, ERR_READ, path, i);
 				} else {
 					stats.date = time(NULL);
 					fwrite_cstats(csts, &stats);
 					rolloverstats(&stats);
+					backup(path, 90, /* rename: */false);
 					if(!fwrite_dstats(dsts, &stats, __FUNCTION__))
-					errormsg(WHERE, ERR_WRITE, "dsts.ini", i);
+						errormsg(WHERE, ERR_WRITE, path, i);
 				}
 				fclose_dstats(dsts);
 				fclose_cstats(csts);
 			} 
 		}
-
+	}
 	if(cfg.node_num==0)	/* called from event_thread() */
 		return(0);