Added write event handler reset in ngx_http_named_location().

On internal redirects this happens via ngx_http_handler() call, which is
not called on named location redirect.  As a result incorrect write handler
remained (if previously set) and this might cause incorrect behaviour (likely
request hang).

Patch by Yichun Zhang (agentzh).

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 42dd664..29b918e 100644
--- a/src/http/ngx_http_core_module.c
+++ b/src/http/ngx_http_core_module.c
@@ -2599,6 +2599,7 @@
 
             r->phase_handler = cmcf->phase_engine.location_rewrite_index;
 
+            r->write_event_handler = ngx_http_core_run_phases;
             ngx_http_core_run_phases(r);
 
             return NGX_DONE;