BUG/MINOR: http-act: Set stream error flag before returning an error

In action_http_set_status(), when a rewrite error occurred, the stream error
flag must be set before returning the error.

No need to backport this patch except if commit 333bf8c33 ("MINOR: http-rules:
Set SF_ERR_PRXCOND termination flag when a header rewrite fails") is
backported. This bug was reported in issue #491.
diff --git a/src/http_act.c b/src/http_act.c
index 40af1ea..dc8c33d 100644
--- a/src/http_act.c
+++ b/src/http_act.c
@@ -305,9 +305,9 @@
 			_HA_ATOMIC_ADD(&__objt_server(s->target)->counters.failed_rewrites, 1);
 
 		if (!(s->txn->req.flags & HTTP_MSGF_SOFT_RW)) {
-			return ACT_RET_ERR;
 			if (!(s->flags & SF_ERR_MASK))
 				s->flags |= SF_ERR_PRXCOND;
+			return ACT_RET_ERR;
 		}
 	}