BUG/MEDIUM: stream: do not try to free a failed stream-conn

In stream_free() if we fail to allocate s->scb() we go to the path where
we try to free it, and it doesn't like being called with a null at all.
It's easily reproducible with -dMfail,no-cache and "tune.fail-alloc 10"
in the global section.

This must be backported to 2.6.
diff --git a/src/stream.c b/src/stream.c
index b2428e4..d37cefa 100644
--- a/src/stream.c
+++ b/src/stream.c
@@ -582,8 +582,8 @@
  out_fail_accept:
 	flt_stream_release(s, 0);
 	LIST_DELETE(&s->list);
- out_fail_alloc_scb:
 	sc_free(s->scb);
+ out_fail_alloc_scb:
  out_fail_attach_scf:
 	task_destroy(t);
  out_fail_alloc: