BUG/MINOR: stream: Fix how backend-specific analyzers are set on a stream

When the stream's backend was defined, the request's analyzers flag was always
set to 0 if the stream had no listener. This bug was introduced with the filter
API but never triggered (I think so).

Because of the commit 5820a366, it is now possible to encountered it. For
example, this happens when the trace filter is enabled on a SPOE backend. The
fix is pretty trivial.

This fix must be backported to 1.7.
1 file changed