The assertion failure was triggered in a debug code-path that validates
property types for internal classes.
zend_verify_internal_read_property_type was called with retval being a
reference, which is not allowed because that function eventually calls to
i_zend_check_property_type, which does not expect a reference.
The non-debug code-path already takes into account that retval can be a
reference, as it optionally dereferences retval.
Add a dereference in zend_verify_internal_read_property_type just before
the call to zend_verify_property_type, which is how other callers often
behave as well.
0801c567dc