getPreviousReleaseVersion should not fail if it runs into a `.RELEASE` version name

[jzheaux]

For the last few releases, the build integration with https://projects.spring.io has failed to delete the old documentation version links for supported-at-the-time Spring LDAP versions.

This was due to 2.3.8.RELEASE being on the list of links. Since it was not in a recognized pattern, it failed.

I wonder if it should simply ignore versions that it doesn't recognize. It could fail if it finds no version at all.

Or better, maybe the task should include x.y.z.RELEASE as a supported pattern.