Post to all existing and non-existing consumers of the buffer

Previously, producer only post to all current clients of the buffer
except for the producer itself. In this change, producer post to all
existing and non-existing clients of the buffer except for the producer
itself.

Fix: 120869419
Test: Vega is able to recover itself during DON after killing vrcore
or compositor process.
Test: on vega_xr and blueline_xr with the following tests
buffer_hub-test buffer_hub_queue-test dvr_buffer_queue-test
dvr_api-test libdvrtracking-test(vega only) buffer_hub_queue_producer-test

Change-Id: I29f24268b7704fbeb06a4302b11dcd89dd13c133