[GIT-PULLS] [php-src] PR #22640: Fix GH-15375: nested "yield from" skips items after valid()/next()

Pull Request: https://github.com/php/php-src/pull/22640
Author: iliaal

Nested `yield from` drops the inner generator's current value on the second and later delegations when it was primed via `valid()`/`next()`. The `ZEND_GENERATOR_DO_INIT` guard in `zend_generator_resume()` reads the flag on `orig_generator`, but in a nested chain the fresh delegation is established by the middle generator, whose flag it never checks. Track and check the delegating generator instead.

Fixes #15375