fix: reused field crash in PartIndices (#15351)

`PartIndices` may be set if xlMetaV2Version is reused.

Clear before unmarshaling and add sanity check when reading.

cmd/xl-storage-format-v2.go

@@ -575,7 +575,7 @@ func (j xlMetaV2Object) ToFileInfo(volume, path string) (FileInfo, error) {
 			fi.Parts[i].ETag = j.PartETags[i]
 		}
 		fi.Parts[i].ActualSize = j.PartActualSizes[i]
-		if len(j.PartIndices) > 0 {
+		if len(j.PartIndices) == len(fi.Parts) {
 			fi.Parts[i].Index = j.PartIndices[i]
 		}
 	}