Brotli: reinterpret_cast from nullptr_t to char * is not allowed.

Found on FreeBSD with -std=c++11.

Signed-off-by: Piotr Sikora <piotrsikora@google.com>

src/ngx_http_brotli_filter_module.cc

diff --git a/src/ngx_http_brotli_filter_module.cc b/src/ngx_http_brotli_filter_module.cc
index 1202d75..43d0a2b 100644
--- a/src/ngx_http_brotli_filter_module.cc
+++ b/src/ngx_http_brotli_filter_module.cc
@@ -788,7 +788,7 @@
         return reinterpret_cast<char *>(NGX_CONF_ERROR);
     }
 
-    return reinterpret_cast<char *>(NGX_CONF_OK);
+    return NGX_CONF_OK;
 }
 
 
@@ -820,7 +820,7 @@
         if (wsize == *np) {
             *np = wbits;
 
-            return reinterpret_cast<char *>(NGX_CONF_OK);
+            return NGX_CONF_OK;
         }
 
         wbits--;