veyron/examples/tunnel: Fix possible "send on closed channel" error.

This is an attempt to fix a race that sometimes leads to a panic of the form:
panic: runtime error: send on closed channel

goroutine 71 [running]:
runtime.panic(0x3c6098, 0x60734e)
	/usr/local/google/home/andreser/veyron/environment/go/src/pkg/runtime/panic.c:279 +0x1a0
veyron/examples/tunnel/tunneld/impl.(*ioManager).stdout2outchan(0x10a2bd70)

Change-Id: I1cb048a09b38defd0f7f06540f05df1d647e234c
2 files changed
tree: 010714018b9be65a37ccd26ad09de7d9f8a78fb6
  1. examples/
  2. lib/
  3. products/
  4. runtimes/
  5. security/
  6. services/
  7. tools/