Router: fixed segmentation fault.

In the case that routes or upstreams is empty and the pass option is a variable.
If the resolved pass is routes or upstreams, a segment error occurred.

src/nxt_http_route.c

@@ -1567,6 +1567,10 @@ nxt_http_route_find(nxt_http_routes_t *routes, nxt_str_t *name,
 {
     nxt_http_route_t  **route, **end;
 
+    if (routes == NULL) {
+        return NXT_DECLINED;
+    }
+
     route = &routes->route[0];
     end = route + routes->items;
 

src/nxt_upstream.c

@@ -78,6 +78,10 @@ nxt_upstream_find(nxt_upstreams_t *upstreams, nxt_str_t *name,
     uint32_t        i, n;
     nxt_upstream_t  *upstream;
 
+    if (upstreams == NULL) {
+        return NXT_DECLINED;
+    }
+
     upstream = &upstreams->upstream[0];
     n = upstreams->items;
 

test/test_variables.py

@@ -100,6 +100,25 @@ class TestVariables(TestApplicationProto):
         assert self.get(url='/1')['status'] == 200
         assert self.get(url='/2')['status'] == 404
 
+    def test_variables_empty(self):
+        def update_pass(prefix):
+            assert 'success' in self.conf(
+                {
+                    "listeners": {
+                        "*:7080": {"pass": prefix + "/$method"},
+                    },
+                },
+            ), 'variables empty'
+
+        update_pass("routes");
+        assert self.get(url='/1')['status'] == 404
+
+        update_pass("upstreams");
+        assert self.get(url='/2')['status'] == 404
+
+        update_pass("applications");
+        assert self.get(url='/3')['status'] == 404
+
     def test_variables_invalid(self):
         def check_variables(routes):
             assert 'error' in self.conf(