FTP: Disallow direct FTPConnection construction

Similar to other resource to object migrations, `FTPConnection` class is not allowed to be constructed with `new FTPConnection`.
Related to b4503fbf88.

Closes GH-6533.

ext/ftp/php_ftp.c

@@ -82,6 +82,11 @@ static zend_object* ftp_object_create(zend_class_entry* ce) {
 	return zobj;
 }
 
+static zend_function *ftp_object_get_constructor(zend_object *zobj) {
+	zend_throw_error(NULL, "Cannot directly construct FTPConnection, use ftp_connect() or ftp_ssl_connect() instead");
+	return NULL;
+}
+
 static void ftp_object_destroy(zend_object *zobj) {
 	php_ftp_object *obj = ftp_object_from_zend_object(zobj);
 
@@ -114,6 +119,7 @@ PHP_MINIT_FUNCTION(ftp)
 
 	memcpy(&ftp_object_handlers, &std_object_handlers, sizeof(zend_object_handlers));
 	ftp_object_handlers.offset = XtOffsetOf(php_ftp_object, std);
+	ftp_object_handlers.get_constructor = ftp_object_get_constructor;
 	ftp_object_handlers.dtor_obj = ftp_object_destroy;
 	ftp_object_handlers.clone_obj = NULL;
 

ext/ftp/tests/ftp_constructor.phpt

@@ -0,0 +1,15 @@
+--TEST--
+Attempt to instantiate an FTPConnection directly
+--SKIPIF--
+<?php
+require 'skipif.inc';
+--FILE--
+<?php
+
+try {
+    new FTPConnection();
+} catch (Error $ex) {
+    echo "Exception: ", $ex->getMessage(), "\n";
+}
+--EXPECT--
+Exception: Cannot directly construct FTPConnection, use ftp_connect() or ftp_ssl_connect() instead