avoid no such cpd or cpx file

https://github.com/chrislusf/seaweedfs/issues/2928

weed/storage/volume_vacuum.go

@@ -135,13 +135,20 @@ func (v *Volume) CommitCompact() error {
 			}
 		}
 		var e error
-		if e = os.Rename(v.FileName(".cpd"), v.FileName(".dat")); e != nil {
+		cpdFile := v.FileName(".cpd")
+		if _, err := os.Stat(cpdFile); err == nil {
+			if e = os.Rename(cpdFile, v.FileName(".dat")); e != nil {
 				return fmt.Errorf("rename %s: %v", v.FileName(".cpd"), e)
 			}
-		if e = os.Rename(v.FileName(".cpx"), v.FileName(".idx")); e != nil {
+
+		}
+		cpxFile := v.FileName(".cpx")
+		if _, err := os.Stat(cpdFile); err == nil {
+			if e = os.Rename(cpxFile, v.FileName(".idx")); e != nil {
 				return fmt.Errorf("rename %s: %v", v.FileName(".cpx"), e)
 			}
 		}
+	}
 
 	//glog.V(3).Infof("Pretending to be vacuuming...")
 	//time.Sleep(20 * time.Second)