Again, unless given a hint, mdds always starts a search from the beginning
of the container, so iterating over a column becomes quadratic.
Shows when selecting (the title of) a large column with different value types,
e.g. in tdf#120558, which triggers setting the selection from
VclQt5Clipboard::setContents(), which calls this.

Change-Id: Ida009c5ddf18ccdc8dff88c15530cc7e33ce80e7
Reviewed-on: https://gerrit.libreoffice.org/72366
Tested-by: Jenkins
Reviewed-by: Luboš Luňák <l.lunak@collabora.com>