Ensure UMO is added to current media

Small fix, when apps post same notification for many times sometimes
active field is false and then converted to true in the next post.
Therefore, it is better to compare the size of current media not the
sorted media.

Flag: com.android.systemui.scene_container
Bug: 326408371
Test: atest SystemUiRoboTests:MediaFilterRepositoryTest
Change-Id: Ib05b4d35a3614976692330d9ff56d82469d7ec85