Fix GH-23301: nested "yield from" repeats a value after "yield from []" - #23302

GH-15375's fix made the DO_INIT re-advance guard in zend_generator_resume() read the flag from the delegating generator rather than from orig_generator. That flag is set by zend_generator_yield_from() and only ever cleared on orig_generator, so on a middle generator it stays set for the rest of its life.

When such a middle generator then delegates to a non-generator iterable (yield from []), it still sits on a ZEND_YIELD_FROM opline, so it is picked as the delegator even though no new generator link was established, and its stale DO_INIT suppresses the resume. The value it yielded last is presented a second time. Twig hits this on every template, since doDisplay() always ends with yield from [];.

Only treat the generator as the delegator when it actually delegated to another generator (node.parent is set); otherwise keep orig_generator as before. The GH-15375 tests still pass.

Fixes GH-23301