[infra-tests] [wptrunner] Guard against empty command_queue in BrowserManager.send_message (#5774)

This happens when sending the message `'init_failed'` and causes wptrunner to hang since `self.command_queue` doesn't exist at that point.

This patch is something I'm using to keep wptrunner from getting stuck, but there is probably a cleaner solution.

View on GitHub: https://github.com/w3c/web-platform-tests/pull/5774

Received on Wednesday, 3 May 2017 22:57:51 UTC