Fix GH-16359 curl write callback crash on FCC usage w/o user function.

Author: devnexen

Zend/zend_API.h

@@ -843,6 +843,9 @@ static zend_always_inline void zend_call_known_fcc(
 	const zend_fcall_info_cache *fcc, zval *retval_ptr, uint32_t param_count, zval *params, HashTable *named_params)
 {
 	zend_function *func = fcc->function_handler;
+	if (UNEXPECTED(!func)) {
+		return;
+	}
 	/* Need to copy trampolines as they get released after they are called */
 	if (UNEXPECTED(func->common.fn_flags & ZEND_ACC_CALL_VIA_TRAMPOLINE)) {
 		func = (zend_function*) emalloc(sizeof(zend_function));