Do not queue trivial buffer for unsupported screenshot request.

When screenshot is not supported, we queue an empty buffer to the
requesting producer. Besides returning a useless screenshot, this
overwrites the valuable error code, returning ERROR_OK whenever we
successfully return the trivial buffer.

Instead, refuse to queue the trivial buffer, and return the original
error code.

This replaces the workaround proposed in
I6da5d2fdecdef6c87d4dd7b353e2464678800110

BUG:27505438
Change-Id: I597a9be25071d2a6ddafb7d39cc1b09fb48d5fd0