Fix arg zval leak in extract_callback_user_func#56
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The callback ZVAL_STRINGL's the chunk into `arg` but only released it on the success path. Both early returns — when zend_fcall_info_init() fails and when zend_call_function() fails — returned without dtoring `arg`, leaking one zend_string per chunk. The init-failure path is reachable from userland by passing a non-callable as the extract callback. zend_fcall_info_argn() ZVAL_COPYs the argument into fci.params (its own ref), so the original `arg` always needs exactly one zval_ptr_dtor. Release it on every path; dtor `retval` only on success, where the engine has actually written it.
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extract_callback_user_funcZVAL_STRINGL's each decoded chunk intoargbut only freed it on the success path. Both early returns leaked onezend_stringper chunk:zend_fcall_info_init()failure (reachable from userland by passing a non-callable as the callback) andzend_call_function()failure.zend_fcall_info_argn()takes its own reference viaZVAL_COPY, so the caller'sargalways needs exactly onezval_ptr_dtor.Release
argon every path; dtorretvalonly on the success path, where the engine has populated it.