Fixed segfault in try_files with nested location.

If memory allocation of a new r->uri.data storage failed, reset its length as
well.  Request URI is used in ngx_http_finalize_request() for debug logging.

src/http/ngx_http_core_module.c

diff --git a/src/http/ngx_http_core_module.c b/src/http/ngx_http_core_module.c
index 7e40e78..b5be1ff 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -1353,6 +1353,7 @@
             r->uri.len = alias + path.len;
             r->uri.data = ngx_pnalloc(r->pool, r->uri.len);
             if (r->uri.data == NULL) {
+                r->uri.len = 0;
                 ngx_http_finalize_request(r, NGX_HTTP_INTERNAL_SERVER_ERROR);
                 return NGX_OK;
             }