bug#37242: orgtbl-to-tsv drops empty cell

[Tak Kunihiro]

Dear Bastien,

>> When org-mode table is converted to tab delimited text using
>> orgtbl-to-tsv, empty cell is dropped out.  I think this is bug.
>>
>> GNU Emacs 26.3 (build 1, x86_64-w64-mingw32) of 2019-08-29
>> runemacs -Q
>> (require 'org-table)
>> (orgtbl-to-tsv '(("aaa") ("bbb") ("") ("ddd")) nil) ; => "aaa\nbbb\nddd"
>> (orgtbl-to-tsv '(("aaa") ("bbb") ("") ("ddd")) '(:backend ascii)) ; => " aaa 
>> \n bbb \n     \n ddd "
> 
> (orgtbl-to-tsv '(("aaa") ("bbb") ("") ("ddd")) nil) returns the same
> output than orgtbl-to-csv, which is to ignore empty *lines* when the
> backend is not set ("nil" here).
> 
> I don't think this is a bug.
> 
> (orgtbl-to-tsv '(("aaa" "AAA") ("bbb" "BBB") ("" "") ("ddd" "DDD")) nil)
> returns something sensible.

What orgtbl-to-tsv/csv does is to convert delimiters.  In my opinion,
to drop out empty lines is overwork.

This comes from orgtbl-to-generic.  I cannot tell the behavior from
docstring.  If this is not a bug, I feel like this behavior is random
one.