`start_type + end_type < 2*IS_STRING` is not right, in this test case
the types are start_type==5 (IS_DOUBLE), end_type==7 (IS_ARRAY).
The IS_ARRAY type is a sentinel to disambiguate single-byte strings.
The path must be taken when one of the types is not a string nor a
single-byte string. Therefore, use < IS_STRING with an OR condition.
Closes GH-13105.
