Update 404.php

It appears as if multiple things are being attempted on the same line:
There is a malformed Ternary Operator
There is an if presumably to check the existence of posts which hands off to a while which would perform the same check with the benefit of looping through the responses.

Lastly, there is a call to the_post() which does not appear to be attached to anything, as it is a 404 response to begin with.