Steps to reproduce:
1) Clone an existing template
2) Edit the clone, submit changes
3) Edit the clone, submit changes
4) Go to the history tab
5) Pick a revision and click revert

Expected results:
The editor contains the template in its previous state

Actual results:
The editor contains an error, see attachments

Found in develop@6f15c1ed72e6d9cd94b23f93cc0d1d4d0f2842a5