Treat apps without recommended versions gracefully

In some edge cases, an app might not have a recommended version.

This is a bit of an edge case, but possible in an index. If the marketvercode (current version code) is 10 but only a version with versioncode 20 is available, F-Droid won't mark that version as suggested.

Hence, UI brokenness ensues - see the screenshots in #326 (closed).