extractor: Fix extraction in symlinked locations

The "The file is not a directory" error is returned in case the archive has common prefix, which have not been changed over the decide-destination signal and the destination is a symlink. This is regression caused by the commit b9590ab7. It causes that the security checks, which was added by the commit 8109c368, verifies also the destination directory by mistake. Let's partially rework the problematic commit to avoid this regression.

Fixes: #36 (closed)