Don't associate a single fd with both channel out and err

[ichizok]

fixes #579 (maybe there is more)

When register a single fd to dispatch-source twice (as ch-out and ch-err), the order of dispatching read-event of ch-out and ch-err cannot be determined.
Meanwhile, write-to-buffer is executed in the order of ch-out and ch-err.

1. receive read-event from ch-err ... (A)
2. receive read-eventfrom ch-out ... (B)
3. write the content of ch-out (B) to buffer
4. write the content of ch-err (A) to buffer

In this way the content of buffer becomes messed up.

Therefore, a single fd should be handled by a single handler.

[splhack]

👍
can we send it to upstream? or can we have #ifdef FEAT_GUI_MACVIM around the modification?

[ichizok]

I think it also needs for upstream, but I'd like to present together other fixes.
So we should apply it prior to upstream since there is marked problem(s) especially for MacVim GUI.

[splhack]

do you mind to add #ifdef FEAT_GUI_MACVIM in order to keep the original code? it will help merging future.

[ichizok]

I updated PR: modified the patch and added #ifdef FEAT_GUI_MACVIM.

[splhack]

👍