Header names are case insensitive, some server uses mixed case
instead.

Change-Id: I0c3d70edabf9ca5ceec0158be99351bf93249461
Reviewed-on: https://gerrit.libreoffice.org/26601Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Giuseppe Castagno <giuseppe.castagno@acca-esse.eu>