If our ssh process has died, not only the next, but all subsequent
calls to clientError() should indicate the error.
restic output when the ssh process is killed with "kill -9":
Save(<data/afb68adbf9>) returned error, retrying after 253.661803ms: Write: failed to send packet header: write |1: file already closed
Save(<data/afb68adbf9>) returned error, retrying after 580.752212ms: ssh command exited: signal: killed
Save(<data/afb68adbf9>) returned error, retrying after 790.150468ms: ssh command exited: signal: killed
Save(<data/afb68adbf9>) returned error, retrying after 1.769595051s: ssh command exited: signal: killed
[...]
error in cleanup handler: ssh command exited: signal: killed
Before this patch:
Save(<data/de698d934f>) returned error, retrying after 252.84163ms: Write: failed to send packet header: write |1: file already closed
Save(<data/de698d934f>) returned error, retrying after 660.236963ms: OpenFile: failed to send packet header: write |1: file already closed
Save(<data/de698d934f>) returned error, retrying after 568.049909ms: OpenFile: failed to send packet header: write |1: file already closed
Save(<data/de698d934f>) returned error, retrying after 2.428813824s: OpenFile: failed to send packet header: write |1: file already closed
[...]
error in cleanup handler: failed to send packet header: write |1: file already closed
dd3b9910ee