fix: ListObjectVersions returning duplicates when resuming with null version id (#19518)

When resuming a versioned listing where `version-id-marker=null`, the `null` object would 
always be returned, causing duplicate entries to be returned.

Add check against empty version

cmd/storage-datatypes.go

@@ -152,6 +152,15 @@ func (f *FileInfoVersions) findVersionIndex(v string) int {
 	if f == nil || v == "" {
 		return -1
 	}
+	if v == nullVersionID {
+		for i, ver := range f.Versions {
+			if ver.VersionID == "" {
+				return i
+			}
+		}
+		return -1
+	}
+
 	for i, ver := range f.Versions {
 		if ver.VersionID == v {
 			return i