fix(*) resolve a possible segfault in the FFI

Creating the `rctx` can happen when no `wasm{}` block is configured
(e.g. through the FFI in `init_worker`). For example,
`set_host_properties_handlers()` might be called (wrong, and unlikely).

Always assume `rctx` might not be created due to a `wasm{}` block, since
the module is wider than Wasm support only.

src/http/ngx_http_wasm_module.c

@@ -584,11 +584,14 @@ ngx_http_wasm_rctx(ngx_http_request_t *r, ngx_http_wasm_req_ctx_t **out)
             rctx->sock_buffer_reuse = loc->socket_buffer_reuse;
             rctx->pwm_lua_resolver = loc->pwm_lua_resolver != NGX_CONF_UNSET
                                      ? loc->pwm_lua_resolver
-                                     : wcf->pwm_lua_resolver;
+                                     : wcf ? wcf->pwm_lua_resolver : NULL;
 
         } else {
             /* fake request */
-            rctx->pwm_lua_resolver = wcf->pwm_lua_resolver;
+
+            if (wcf) {
+                rctx->pwm_lua_resolver = wcf->pwm_lua_resolver;
+            }
         }
     }
 #if (NGX_DEBUG)