BUG/MEDIUM: connections: Don't assume the connection has a valid session.

Don't assume the connection always has a valid session in "owner".
Instead, attempt to retrieve the session from the stream, and modify
the error snapshot code to not assume we always have a session, or the proxy
for the other end.
diff --git a/src/proxy.c b/src/proxy.c
index 8e32564..046b1b5 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -1560,7 +1560,7 @@
 	es->when    = date; // user-visible date
 	es->srv     = objt_server(target);
 	es->oe      = other_end;
-	if (objt_conn(sess->origin) && conn_get_src(__objt_conn(sess->origin)))
+	if (sess && objt_conn(sess->origin) && conn_get_src(__objt_conn(sess->origin)))
 		es->src  = *__objt_conn(sess->origin)->src;
 	else
 		memset(&es->src, 0, sizeof(es->src));
@@ -2234,7 +2234,7 @@
 
 		if (appctx->ctx.errors.iid >= 0 &&
 		    appctx->ctx.errors.px->uuid != appctx->ctx.errors.iid &&
-		    es->oe->uuid != appctx->ctx.errors.iid)
+		    (!es->oe || es->oe->uuid != appctx->ctx.errors.iid))
 			goto next;
 
 		if (appctx->ctx.errors.ptr < 0) {
@@ -2264,15 +2264,15 @@
 					     " frontend %s (#%d): invalid request\n"
 					     "  backend %s (#%d)",
 					     appctx->ctx.errors.px->id, appctx->ctx.errors.px->uuid,
-					     (es->oe->cap & PR_CAP_BE) ? es->oe->id : "<NONE>",
-					     (es->oe->cap & PR_CAP_BE) ? es->oe->uuid : -1);
+					     (es->oe && es->oe->cap & PR_CAP_BE) ? es->oe->id : "<NONE>",
+					     (es->oe && es->oe->cap & PR_CAP_BE) ? es->oe->uuid : -1);
 				break;
 			case 1:
 				chunk_appendf(&trash,
 					     " backend %s (#%d): invalid response\n"
 					     "  frontend %s (#%d)",
 					     appctx->ctx.errors.px->id, appctx->ctx.errors.px->uuid,
-					     es->oe->id, es->oe->uuid);
+					     es->oe ? es->oe->id : "<NONE>" , es->oe ? es->oe->uuid : -1);
 				break;
 			}