PHP: forced initialization of $_SERVER in fastcgi_finish_request().

The "auto_globals_jit" PHP option postponed the initialization of the $_SERVER
global variable until the script using it had been loaded (e. g. via the
"include" expression).  As a result, nxt_php_register_variables() could be
called after fastcgi_finish_request() had finished the request and nulled
ctx->req, which thus caused a segmentation fault.

docs/changes.xml

@@ -44,6 +44,13 @@ points on a per-request basis during static file serving.
 </para>
 </change>
 
+<change type="bugfix">
+<para>
+a segmentation fault might have occurred in the PHP module if
+fastcgi_finish_request() was used with the "auto_globals_jit" option enabled.
+</para>
+</change>
+
 </changes>