Rewrite output file rather than infinitely appending

[nielstron]

At the current state this extension did two terrible things:

• it bloated up the output file by appending the complete new output that was supposed to replace the file
• reading the resulting database file resulting in obtaining the first version that was ever written and discarding all further updates (that were just appended)

This seek fixes both of these issues.

[nielstron]

How did I find this?

• update a database by inserting 1000 elements one-by-one
• result: 1.6GB of data, when reading I obtain a db with a singleton element...
• after this fix: 50MB of data, when reading I obtain a db with 1000 elements

[MrPigss]

You are right. I'm gratefull that you noticed. I have immediatly merged the change.