SF: Apply pending transactions to new sidebands

When a Layer's sideband stream is set, apply any pending transactions.
Otherwise they would never be applied since sideband streams don't
trigger updates by pushing new buffers.

Bug: 20125898
Change-Id: I0c7a91cdf84e6205801f4ab64eee0b09e4c0b3e0
(cherry picked from commit 3b04e1383eca6cb1d43ebe23a421c427007690c7)