Description:
------------
Currently `zend_fake_get_properties` in `ext/ffi/ffi.c` returns a pointer to const HashTable `zend_empty_array`. Attempting to iterate over this array in userland leads to a segfault because PHP tries to increment `zend_empty_array`'s `nIteratorsCount` which is const memory.

The proposed patch allows objects to return NULL for the `get_properties` handler. In this case, the VM skips the foreach block.

If this approach is acceptable, there are other extensions and call sites[1][2] to fix where `zend_empty_array` leaks into userland.

[1] https://github.com/php/php-src/blob/107962208a19d8b6dc1a190cb25fc37614411e71/ext/com_dotnet/com_handlers.c#L221-L229
[2] https://github.com/protocolbuffers/protobuf/issues/7319


Test script:
---------------
<?php

$ffi = FFI::cdef('');

foreach ($ffi as $_) {
}


Expected result:
----------------
no segfault

Actual result:
--------------
segfault