Fix #80186: Prevent segfault when iterating FFI obj props

[adsr]

https://bugs.php.net/bug.php?id=80186

[nikic]

• zend_vm_execute.h is a generated file. You need to change zend_vm_def.h and then run zend_vm_gen.php.
• It looks like this issue also exists on PHP-7.4, so we should target that branch instead.
• Rather than allowing NULL returns, we should do basically what you're doing here, but rather than checking for NULL return, check for an empty array (zend_hash_num_elements(ht) == 0).

[nikic]

Looking at this code, we probably should also add some fast-path skips for empty arrays in more places, as currently we'll end up allocating a new copy of an empty array, just to free it again right away. But that's a separate issue...

[nikic]

I've landed a fix in 15443f8 that does the aforementioned check for empty arrays.

[adsr]

Thanks @nikic Can you add a hacktoberfest-accepted label to this issue?

[nikic]

Sure, done!