Fixed segmentation fault with empty config on Windows.

See here for report:
http://mailman.nginx.org/pipermail/nginx-ru/2011-September/043288.html

src/http/ngx_http.c

diff --git a/src/http/ngx_http.c b/src/http/ngx_http.c
index 4f0b79d..1eb22f8 100644
--- a/src/http/ngx_http.c
+++ b/src/http/ngx_http.c
@@ -1747,10 +1747,12 @@
 
 #if (NGX_WIN32)
     {
-    ngx_iocp_conf_t  *iocpcf;
+    ngx_iocp_conf_t  *iocpcf = NULL;
 
-    iocpcf = ngx_event_get_conf(cf->cycle->conf_ctx, ngx_iocp_module);
-    if (iocpcf->acceptex_read) {
+    if (ngx_get_conf(cf->cycle->conf_ctx, ngx_events_module)) {
+        iocpcf = ngx_event_get_conf(cf->cycle->conf_ctx, ngx_iocp_module);
+    }
+    if (iocpcf && iocpcf->acceptex_read) {
         ls->post_accept_buffer_size = cscf->client_header_buffer_size;
     }
     }