Old db version is lost when aborting upgrade

[gterzian]

https://w3c.github.io/IndexedDB/#abort-an-upgrade-transaction

Set connection’s version to database’s version if database previously existed, or 0 (zero) if database was newly created.

But by then, the db version has already been set to the requested version at https://w3c.github.io/IndexedDB/#upgrade-a-database

Let old version be db’s version.
Set db’s version to version. This change is considered part of the transaction, and so if the transaction is aborted, this change is reverted.

To properly revert the change, oldVersion needs to be stored somewhere that is accessible from #abort-an-upgrade-transaction, for example on the transaction, or passed down as a variable.

[stelar7]

Since the version is considered part of the transaction, explicitly cleaning it in separate steps seems unnecessary imo