Fix empty metadata after message cloning

[msiebeneicher]

The purpose of this pull request

• fixed cloning metadata
• fixed unit test for cloning metadata

Checklist

• make test executed successfully
• unit test provided

[coveralls]

Coverage increased (+0.06%) to 71.652% when pulling f6bc639 on bugfix/fix_empty_meta_data_after_cloning into 892ba2d on master.

[coveralls]

Coverage increased (+0.06%) to 71.652% when pulling f6bc639 on bugfix/fix_empty_meta_data_after_cloning into 892ba2d on master.

[arnecls]

Found and fixed an issue after merging.
The thing with CloneOriginal is that we create a copy of the current state first and then either need to clone the current metadata (to avoid changes "leaking" into the copy) or explicitly set it to nil as the original (as defined by the "freeze" operation) does not have metadata.

See commit: 7c14a24