Cursor protocol cuts off the end of json body for some json functions

Testcase (run MTR test with --cursor-protocol):

select json_array_append('["a", "b"]', '$', FALSE);

Expected result:

json_array_append('["a", "b"]', '$', FALSE)

["a", "b", false]

Actual result:

json_array_append('["a", "b"]', '$', FALSE)

["a", "b", fals

The same behavior repeats for json_insert, json_set, json_type, json_unquote, json_object, json_loose, json_detailed