fix segfault if no http section is defined in confguraiton,
the bug has been introduced in r1259
diff --git a/src/http/ngx_http_config.h b/src/http/ngx_http_config.h
index 6629210..74f6f6c 100644
--- a/src/http/ngx_http_config.h
+++ b/src/http/ngx_http_config.h
@@ -69,8 +69,10 @@
     ((ngx_http_conf_ctx_t *) cf->ctx)->loc_conf[module.ctx_index]
 
 #define ngx_http_cycle_get_module_main_conf(cycle, module)                    \
-    ((ngx_http_conf_ctx_t *)                                                  \
-         cycle->conf_ctx[ngx_http_module.index])->main_conf[module.ctx_index]
+    (cycle->conf_ctx[ngx_http_module.index] ?                                 \
+        ((ngx_http_conf_ctx_t *) cycle->conf_ctx[ngx_http_module.index])      \
+            ->main_conf[module.ctx_index]:                                    \
+        NULL)
 
 
 #endif /* _NGX_HTTP_CONFIG_H_INCLUDED_ */