Fix the segmentation fault while logging the host on the custom HTTP logger

- Seems to be a regression introduced in the commit
  796bfab2317699779bb0d7dca257bb97083399d8 (fix was already done in commit
  ee0b21652b00f9398869b097c3ddceb9f86600a9)
- Doesn't happen with htplib v0.5.6, but it does in the latest, v0.5.9