unit/test-avrcp: Fix using empty response to /TP/PAS/BV-08-C
unit/test-avrcp: Fix using empty response to /TP/PAS/BV-08-C

The purpose of unit tests is to exercise the code as much as possible so
return non-empty when testing avrcp_get_player_values_text_rsp.

ComputeCycles/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,mapfau/bluez,mapfau/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,ComputeCycles/bluez,pkarasev3/bluez,pkarasev3/bluez,silent-snowman/bluez,silent-snowman/bluez,ComputeCycles/bluez,pstglia/external-bluetooth-bluez,pkarasev3/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,silent-snowman/bluez