[BugFix] fix snapshot meta upgrade compatible (StarRocks#23442)

Fixes StarRocks#20436

When the BE try to parse the snapshot generated by old version BE, the snapshot doesn't contain delta column in footer, so parse will fail.

Signed-off-by: luohaha <[email protected]>
Signed-off-by: Moonm3n <[email protected]>

Author: luohaha

be/src/storage/snapshot_meta.cpp

@@ -150,6 +150,10 @@ Status SnapshotMeta::_parse_delta_column_group(SnapshotMetaFooterPB& footer, Ran
         return Status::InternalError(
                 fmt::format("mismatched delta column group size and segment id size, file: {}", file->filename()));
     }
+    if (footer.dcg_offsets_size() == 0) {
+        // this snapshot meta is generated by low version BE.
+        return Status::OK();
+    }
     // Parse delta column group
     std::string buff;
     const int num_dcglists = footer.dcg_offsets_size() - 1;