Fix hang on Windows when multiple --client args are present

Fix hang on Windows when multiple --client args are present

The Windows poll function does not clear revents field before it is
populated.  As a result, subsequent calls to poll using the same
pollfd reference return with revents set even when there is nothing
available to read.  This later results in a hang in recv().

Signed-off-by: James Rizzo <james.rizzo@broadcom.com>