seafile: fix integration test errors by adding dot to encoding

The seafile backend used to be able to cope with files called "." and
".." but at some point became unable to do so, causing integration
test failurs.

This adds EncodeDot to the encoding which encodes "." and ".." names.

backend/seafile/seafile.go

@@ -111,7 +111,8 @@ func init() {
 				encoder.EncodeSlash |
 				encoder.EncodeBackSlash |
 				encoder.EncodeDoubleQuote |
-				encoder.EncodeInvalidUtf8),
+				encoder.EncodeInvalidUtf8 |
+				encoder.EncodeDot),
 		}},
 	})
 }