[ Merge of http://go/wvgerrit/54880 ]
Sending clear subsamples but filtering out encrypted ones,
before the keys have been loaded, causes problems during decode.
This is because subsamples that contain the first and last
subsample flags may be filtered out.
Clear subsamples that have first and last subsample flags set
will still be allowed to be passed to the decoder.
Bug: 110251447
Bug: 73447733
Test: WV Unit/integration tests.
Change-Id: I8c91c88f6313ad7b7b21c1c95e4c5787381949c1