Fix use-of-uninitialized-value of EG(last_fatal_error_backtrace) with ZTS

[iluuu1994]

Static variables are zeroed, but ts memory is not. Hence, we need to do it ourselves.

See https://github.com/php/php-src/actions/runs/13043905843/job/36391169998.

[TimWolla]

Static variables are zeroed, but ts memory is not.

Makes me wonder if the first thing happening in GINIT should be a memset() to avoid this kind of bug.

Patch LGTM. /cc @ericnorris

[iluuu1994]

Hmm... unfortunately executor_globals_ctor() is called twice, once by tsrm_update_active_threads() and once by zend_post_startup(). The ini initialization happens in-between, so fatal_error_backtrace_on is initialized to false again. We could just initialize it to true, but this might lead to slight differences between zts/nts before ini's are loaded.

[iluuu1994]

Honestly, I have no idea why executor_globals_ctor() is being called twice, but I now moved the initialization directly after ts_allocate_fast_id(), which seems to work fine.

[ericnorris]

Sorry, I ended up being a bit busier than usual at the end of last week. Thanks @iluuu1994!