Stronger presence check

- Fixes `out-of-range` on a Tuple
- Ensures `KeyError` doesn't happen for the faulty key. I would argue if someone the script should be re-written to accommodate this in the first place.

safaribooks.py

@@ -174,7 +174,7 @@ def book_info(self, info):
  ("Title", info["title"]), ("Authors", ", ".join(aut["name"] for aut in info["authors"])),
  ("Identifier", info["identifier"]), ("ISBN", info["isbn"]),
  ("Publishers", ", ".join(pub["name"] for pub in info["publishers"])),
- ("Rights", info["rights"]),
+ ("Rights", info["rights"] if "rights" in info and info["rights"] else ""),
  ("Description", description[:500] + "..." if len(description) >= 500 else description),
  ("Release Date", info["issued"]),
  ("URL", info["web_url"])
@@ -961,7 +961,7 @@ def create_content_opf(self):
  escape(self.book_info["description"]),
  subjects,
  ", ".join(escape(pub["name"]) for pub in self.book_info["publishers"]),
- escape(self.book_info["rights"]) if self.book_info["rights"] else "",
+ escape(self.book_info["rights"]) if "rights" in self.book_info and self.book_info["rights"] else "",
  self.book_info["issued"],
  self.cover,
  "\n".join(manifest),