Service: transmits empty station list

In case of bad reception, station lists e.g. for DAB might be empty.
Until now, empty station lists from broadcast radio HAL were ignored
by radio service and not forwarded to radio app.
With this patch, radio service transmits empty station lists from
broadcast radio HAL to radio app.

Bug: 193674842
Test: manual - Bench test with connected radio

Signed-off-by: Tobias Schmidt-Samoa <tschmi63@ford.com>
Change-Id: Ida0d7637e32b4b9064cddbd3e8d8d4b8d347023c