BassClient: Fix not putting empty metadata buffer on the list

The list size has to match the number of subgroups otherwise we would
not be able to connect each subgroup with it's metadata if one of
the subgroups has an empty metadata.

Bug: 150670922
Sponsor: jpawlowski@
Test: tested manually
Merged-In: I7a2a190bc9f8795eab299cece0af0fd5f6e792f0
Change-Id: I7a2a190bc9f8795eab299cece0af0fd5f6e792f0
(cherry picked from commit c420c793)