race condition on downloading REH

[GitMensch]

I see another one that also applies to the open-ssh extension: if you are on Windows and use the "restart for update" option both have the same issue:

• open two or more WSL workspaces to the same WSL instance in parallel
• open two or more OpenSSH workspaces on the same target in parallel

when you now update and restart, those workspaces are opened directly after the start in parallel, the ones that connect to the same machine all find the server directory not being available - and then trying to download the reh file to the same place - the second one seems to interrupt the first one and you end with an invalid target file.

It could be useful to use a synchronization file to work around the race condition here.

Originally posted by @GitMensch in #11 (comment)

[GitMensch]

friendly ping @jeanp413 - this triggers nearly each time a vscode update is done, because I have quite commonly more than one workspace in a given server open, and when the restart triggers the installation in both environments it creates a broken download which is then not re-downloaded.

Note: while the PR #11 won't fix this, it would at least provide a nice workaround - "retry" in a single window, then let it install cleanly, then click on retry in the other window(s).
As noted: this should also be applied in the open ssh one.