Fix reference returned from CallbackFilterIterator::accept()

Fixes oss-fuzz #58181

Author: iluuu1994

Zend/tests/oss_fuzz_58181.phpt

@@ -0,0 +1,14 @@
+--TEST--
+oss-fuzz #58181: Fix unexpected reference returned from CallbackFilterIterator::accept()
+--FILE--
+<?php
+function test(array $data) {
+    $iterator = new ArrayIterator($data);
+    $iterator = new \CallbackFilterIterator($iterator, fn&() => true);
+    $iterator->rewind();
+}
+
+test(['a', 'b']);
+?>
+--EXPECTF--
+Notice: Only variable references should be returned by reference in %s on line %d

ext/spl/spl_iterators.c

@@ -1787,6 +1787,8 @@ PHP_METHOD(CallbackFilterIterator, accept)
 
 	if (zend_call_function(fci, fcc) != SUCCESS || Z_ISUNDEF_P(return_value)) {
 		RETURN_FALSE;
+	} else if (Z_ISREF_P(return_value)) {
+		zend_unwrap_reference(return_value);
 	}
 }
 /* }}} */