Re: [proposal] de-TOAST'ing using a iterator

>> Also, I don't think
>> the new logic for the ctrl/c variables is an improvement:
>>
>> 1. iter->ctrlc is intialized with '8' (even in the uncompressed case,
>> which is confusing). Any time you initialize with something not 0 or
>> 1, it's a magic number, and here it's far from where the loop variable
>> is used. This is harder to read.
>
> `iter->ctrlc` is used to record the value of `ctrl` in pglz_decompress at the end of
> the last iteration(or loop). In the pglz_decompress, `ctrlc`’s valid value is 0~7,
> When `ctrlc` reaches 8,  a control byte is read from the source
> buffer to `ctrl` then set `ctrlc` to 0. And a control bytes should be read from the
> source buffer to `ctrlc` on the first iteration. So `iter->ctrlc` should be intialized with '8'.

My point here is it looks strange out of context, but "0" looked
normal. Maybe a comment in init_detoast_buffer(), something like "8
means read a control byte from the source buffer on the first
iteration, see pg_lzdecompress_iterate()".

Or, possibly, we could have a macro like INVALID_CTRLC. That might
even improve the readability of the original function. This is just an
idea, and maybe others would disagree, so you don't need to change it
for now.

At this point, there are no functional things that I think we need to
change. It's close to ready-for-committer. For the next version, I'd
like you go through the comments and edit for grammar, spelling, and
clarity as you see fit. I know you're not a native speaker of English,
so I can help you with anything that remains.

Also note we use braces
on their own lines
{
    like this
}