Check for request line too-big-ness later, fix spurious 414s

Sometimes this happens:

1. A small request packet comes in

2. A second (big) request packet comes in. Some of it is URI, the rest is not. `::delimit` sees it and is like "holy shit, this thing is too big" and throws a 414.

This fix only kills the conn if we go over the limit *and* `::delimit` didn't find a request line.