rpc: handle stream close gracefully
rpc: handle stream close gracefully

Change-Id: I187f2b9b0b8677023533aa501ca143d50b8e41cf
Reviewed-on: https://upspin-review.googlesource.com/7860
Reviewed-by: Rob Pike <4dc7c9ec434ed06502767136789763ec11d2c4b7@google.com>

upspin/upspin,upspin/upspin