[BUG] http: typos on several unlikely() around header insertion

[BUG] http: typos on several unlikely() around header insertion

In many places where we perform header insertion, an error control
is performed but due to a mistake, it cannot match any error :

   if (unlikely(error) < 0)
instead of
   if (unlikely(error < 0))

This prevents error 400 responses from being sent when the buffer is
full due to many header additions. This must be backported to 1.3.