Return default value T() if no values have been added to the filter.
Together with
https://webrtc-review.googlesource.com/c/src/+/369440, DataRate etc can be used by the filter.
Bug: None
Change-Id: I3d0e1a3e698a91a6197bf434ace2ff8246dc393e
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/369420
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Reviewed-by: Danil Chapovalov <danilchap@webrtc.org>
Commit-Queue: Per Kjellander <perkj@webrtc.org>
Cr-Commit-Position: refs/heads/main@{#43461}
f4ee1a1ef3