fix building by msvc introduced in r1817

src/http/modules/ngx_http_dav_module.c

diff --git a/src/http/modules/ngx_http_dav_module.c b/src/http/modules/ngx_http_dav_module.c
index 09dac0e..e597923 100644
--- a/src/http/modules/ngx_http_dav_module.c
+++ b/src/http/modules/ngx_http_dav_module.c
@@ -1140,7 +1140,7 @@
      *     conf->methods = 0;
      */
 
-    conf->min_delete_depth = NGX_CONF_UNSET;
+    conf->min_delete_depth = NGX_CONF_UNSET_UINT;
     conf->access = NGX_CONF_UNSET_UINT;
     conf->create_full_put_path = NGX_CONF_UNSET;