wireprotov1peer: don't raise internal errors in some cases
Specifically, when the peer is closed in the middle of a batch of rpcs.
Differential Revision: https://phab.mercurial-scm.org/D10074
sshpeer: don't fail forwarding output from closed connections
The test still shows an internal error, but one that happens
further along.
Differential Revision: https://phab.mercurial-scm.org/D10073