sink-input,source-output: Handle devices going away in unlink hooks

If a *_UNLINK_POST hook causes a sink-input/source-output's sink/source
to go away, the subsequent attempt to update the sink/source status will
cause an assert. We deal with this by checking the sink/source status
before trying to update it.

src/pulsecore/source-output.c

@@ -587,7 +587,9 @@ void pa_source_output_unlink(pa_source_output*o) {
     }
 
     if (o->source) {
-        pa_source_update_status(o->source);
+        if (PA_SOURCE_IS_LINKED(pa_source_get_state(o->source)))
+            pa_source_update_status(o->source);
+
         o->source = NULL;
     }