Fix off-by-one memory issue.

It was resulting in garbage characters with certain semvers with patch
versions. Regression tests with the patch version "release1" replicate the
issue. My thanks again to Andrew "RhodiumToad" Gierth for pointing out the
lack of `+1` in a call to `palloc()` that was the underlying cause of the
problem.
Increment extension to v0.4.0.