[#2875][Web] Fix: WebUI Json dumps Error

* A torrent file contains an uncommon field 'filehash' which must be hex encoded
   to allow dumping the torrent info to json. Otherwise it will fail with:
   UnicodeDecodeError: 'utf8' codec can't decode byte 0xe5 in position 0: invalid continuation byte

deluge/ui/common.py

@@ -113,6 +113,8 @@ class TorrentInfo(object):
                     f["sha1"] = f["sha1"].encode('hex')
                 if "ed2k" in f and len(f["ed2k"]) == 16:
                     f["ed2k"] = f["ed2k"].encode('hex')
+                if "filehash" in f and len(f["filehash"]) == 20:
+                    f["filehash"] = f["filehash"].encode('hex')
                 paths[path] = f
                 dirname = os.path.dirname(path)
                 while dirname: