German dselect translation update

Update to 278t.
po: Update Catalan translations
dpkg-shlibdeps: Handle empty minimum versions when initializing them

If the minimum version is empty (which means it was 0), we cannot use it
to compare against the existing minimum version if that exists, and we
should not be overwritting that, either.

Regression introduced in commit 51c55641fb6c66e149ea93c344cb788c68978c75.

Closes: #764929
Release 1.17.18
Bump version to 1.17.19