When "arc" receives SIGWINCH or other signals during display of a prompt, recover

Summary:
Ref T13546. Resizing the terminal window to send SIGWINCH, or other signals, may interrupt "stream_select()" with an error which upgrades to a RuntimeException.

When "stream_select()" fails, continue and test the stream itself.

Test Plan: Waited for a prompt, resized the window. Before patch: SIGWINCH interruption. After patch: undisturbed prompt.

Maniphest Tasks: T13546

Differential Revision: https://secure.phabricator.com/D21317