jottacloud: fix server-side copy onto a trashed file failing as corrupted

When a server-side copy landed on a file that was in the trash, rclone
restored it with a zero creation and modification time unless
--metadata was in use. The server then returned a time which couldn't be
parsed, the copy was reported as having size 0 and failed with
"corrupted on transfer".

The restored file now gets the source's times, as it did before
metadata support was added.

backend/jottacloud/jottacloud.go

@@ -1500,9 +1500,9 @@ func (f *Fs) Copy(ctx context.Context, src fs.Object, remote string) (fs.Object,
 	info, err := f.copyOrMove(ctx, "cp", srcObj.filePath(), remote)
 
 	if err == nil {
-		var createTime time.Time
+		createTime := srcObj.createTime
 		var createTimeMeta bool
-		var modTime time.Time
+		modTime := srcObj.modTime
 		var modTimeMeta bool
 		if meta != nil {
 			createTime, createTimeMeta = srcObj.parseFsMetadataTime(meta, "btime")