fix regression bug in HTTPClient FS#2621

In the recent refactoring of the HTTPClient, a problem with certain
systems was reintroduced. On these systems a select() call always
waits for a timeout on the first call before working properly on the
second call.

This patch reintroduces the shorter timeouts with usleep rate limiting
again.

Since this bug is not reproducible on other systems it can't be unit
tested unfortunately.