bug#71049: async-shell-command ends with "Process *Async Shell Command* finished" when remote "direct-async-process"

[Dmitry Gutov <dmitry@gutov.dev>]

Previously mentioned in bug#70901.

When a Tramp connection is configured as "direct-async-process",

1. If the buffer *Async Shell Command* does not exist, invoking M-& in a 
remote buffer from that connection makes it end with

   Process *Async Shell Command* finished

The command can be simple, like 'ls' or 'echo 123'. I also see this 
added to *Messages*:

   Tramp: Inserting 
‘/ssh:dgutov@fencepost.gnu.org:/home/d/dgutov/.tramp_history’...done

Which seems odd (tramp history is re-read every time like this, for some 
purpose?).

2. If the buffer such named already exists when command is invoked, then 
this doesn't happen (the output seems correct). But *Messages* says

   -l: finished.

...which is a big puzzling as well.

Also, scenario 1 (when the buffer doesn't exist yet) takes longer than 
2, but that might be a side-effect of implementation external to Tramp.