fetch: don't use pooled buffer in body mixin

[tsctx]

completely fix #3337

[tsctx]

@mcollina
there are many such cases, should they be fixed?

[KhafraDev]

I think there's still some questions left to answer here. Mostly: is this something we need? If not (and I am assuming we don't), what benefit is there in adding it?

[tsctx]

is this something we need? If not (and I am assuming we don't), what benefit is there in adding it?

I also have my doubts. but, double cloning can be avoided, as in the commit just added.

In fact, it is not skipping the spec, but creating a new arraybuffer at safeBufferConcat according to this, which should not be a violation of the spec.

[KhafraDev]

I'm not interested in any solution that changes around the steps in the spec

[tsctx]

Hmm... If I was to say it, It is completely fix #3337, but we may not need to worry about pooled buffer.