linkbot: Minor fix with log message

Returned value could be None, so this accounts for that

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

plugins/linkbot.py

@@ -144,7 +144,10 @@ class Linkbot(Plugin):
                 continue
             # Fetch the HTML at the URL
             result = await self.fetch(url)
-            log.debug("got %s characters back", len(result))
+            if result:
+                log.debug("got %s characters back", len(result))
+            else:
+                log.debug("got nothing back")
             if not result:
                 # Could not fetch this URL
                 log.debug("skipping URL %s because it couldn't be fetched", url)