pcloud: Fix rclone link for files

This was only working for files in the root directory and wasn't
looking at the encoding.

This is fixed to use NewObject which takes both things into account
and it makes the share by ID instead of by path.

This problem was spotted by the integration tests.

backend/pcloud/pcloud.go

@@ -814,14 +814,19 @@ func (f *Fs) linkDir(ctx context.Context, dirID string, expire fs.Duration) (str
 }
 
 func (f *Fs) linkFile(ctx context.Context, path string, expire fs.Duration) (string, error) {
+	obj, err := f.NewObject(ctx, path)
+	if err != nil {
+		return "", err
+	}
+	o := obj.(*Object)
 	opts := rest.Opts{
 		Method:     "POST",
 		Path:       "/getfilepublink",
 		Parameters: url.Values{},
 	}
 	var result api.PubLinkResult
-	opts.Parameters.Set("path", path)
+	opts.Parameters.Set("fileid", fileIDtoNumber(o.id))
-	err := f.pacer.Call(func() (bool, error) {
+	err = f.pacer.Call(func() (bool, error) {
 		resp, err := f.srv.CallJSON(ctx, &opts, nil, &result)
 		err = result.Error.Update(err)
 		return shouldRetry(resp, err)
@@ -834,11 +839,6 @@ func (f *Fs) linkFile(ctx context.Context, path string, expire fs.Duration) (str
 
 // PublicLink adds a "readable by anyone with link" permission on the given file or folder.
 func (f *Fs) PublicLink(ctx context.Context, remote string, expire fs.Duration, unlink bool) (string, error) {
-	err := f.dirCache.FindRoot(ctx, false)
-	if err != nil {
-		return "", err
-	}
-
 	dirID, err := f.dirCache.FindDir(ctx, remote, false)
 	if err == fs.ErrorDirNotFound {
 		return f.linkFile(ctx, remote, expire)