Fix uninitialized read in rfc1867 handler reported by valgrind. Only in PHP 5.6.

This commit fixes initialized read, but calling php_session_initialize() directly
is problematic because configuration could be invalid. Invalid config may result
in segfault. This will be addressed later.

ext/session/session.c

@@ -96,6 +96,7 @@ static inline void php_rinit_session_globals(TSRMLS_D) /* {{{ */
 	PS(session_status) = php_session_none;
 	PS(mod_data) = NULL;
 	PS(mod_user_is_open) = 0;
+	PS(defined_sid) = 1;
 	/* Do NOT init PS(mod_user_names) here! */
 	PS(http_session_vars) = NULL;
 }