[PATCH] encodedstream: Don't query VAAPI in the constructor

[PATCH] encodedstream: Don't query VAAPI in the constructor

Querying VAAPI is expensive, so we should only do that when necessary.
So rather than querying what encoder to use on construction, query it on
start and only if we don't already have an encoder set. This also avoids
duplicate lookups if the user already set the encoder.

Gbp-Pq: Name upstream_8793ae86_encodedstream-Don-t-query-VAAPI-in-the-constructor.patch