Skip showing the Smartspace recommendation card if it's an empty update.

Smartspace always sends out an update on headphones connection for a reliable triggering:
- A valid recommendation list with >= 3 items;
- Otherwise, an empty list only for triggering.

If it's the latter case, the recommendation should not be shown.

Fixes: 186585554
Test: Studio builds
Change-Id: I441454809f7c6b10e21d18f46c10e01efc892db0