Make troves asking for the horn of Geryon take it from players

With the somewhat recent changes to the horn (0.14-a0-1887-g5c01cd8 and
0.14-a0-2885-ge2f36c2 in particular) bringing it much closer to an
ordinary item than to the like of runes of Zot, this might be better.
The implementation in-code however most certainly is not better at this
point. Perhaps somebody would like to make that a bit prettier.
Make that a bit prettier.