Fixup concurrency on mediation runs and stats, improving tutorial CdrStats files

engine/mediator.go

@@ -175,11 +175,11 @@ func (self *Mediator) RateCdr(storedCdr *utils.StoredCdr, sendToStats bool) erro
 			}
 		}
 		if sendToStats && self.stats != nil { // We send to stats only after saving to db since there are chances we cannot store and then no way to reproduce stats offline
-			go func() {
+			go func(cdr *utils.StoredCdr) { // Pass it by value since the variable will be overwritten by for
 				if err := self.stats.AppendCDR(cdr, nil); err != nil {
 					Logger.Err(fmt.Sprintf("Could not append cdr to stats (mediator): %s", err.Error()))
 				}
-			}()
+			}(cdr)
 		}
 	}
 	return nil