Description:
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CachingIterator doesn't work if its innerIterator is an instance of IteratorIterator.

The use-case provided here might seem strange as the IteratorIterator is not necessary.
However, it would become necessary for a use case dealing with a Traversable class such as PDOStatement, and the bug stays the same.

Additionnaly, we actually have to call next() manually but it should be called internaly.
This leads to another bug which has already been reported at #46227

Reproduce code:
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$it = new ArrayIterator(range('a','z');
$cache = new CachingIterator(new IteratorIterator($it));
$cache->next();
var_dump($cache->current());
var_dump($cache->hasNext());

Expected result:
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1 and TRUE

Actual result:
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NULL and FALSE