[Woo POS][Non-Simple Products] Handle empty variations state

[AnirudhBhat]

The goal of this task is to handle empty variations state - Display proper empty screen similar to products when a variable product has no variations.

Decision: pdfdoF-62l-p2#comment-7224

[dangermattic]

Thanks for reporting! 👍

[wpmobilebot]

Version 21.4 has now entered code-freeze, so the milestone of this PR has been updated to 21.5.