[Web] Change request.base path encoding to utf-8

A user reported a problem with setting base path resulting in this error:

    encoding with 'idna' codec failed (UnicodeError: label too long)

It is likely the base path is longer than 63 chars, which is unusual,
however the idna codec is for domain name not paths so switch to utf-8.

Fixes: #3261

CHANGELOG.md

@@ -6,6 +6,7 @@
 
 - Fix TypeError in Peers Tab setting country flag.
 - Fix reverse proxy header TypeError (#3260).
+- Fix request.base 'idna' codec error (#3261).
 
 ### Documentation
 

deluge/ui/web/server.py

@@ -583,7 +583,7 @@ class TopLevel(resource.Resource):
         if base[-1] != '/':
             base += '/'
 
-        request.base = base.encode('idna')
+        request.base = base.encode('utf-8')
 
         return resource.Resource.getChildWithDefault(self, path, request)