See
<https://msdn.microsoft.com/en-us/library/dd183374%28v=vs.85%29.aspx>
for more info about the header structure that has to be prepended to the
real data to make our BMP import filter happy.

Change-Id: Iabdf4cd169b82ea951d1c1b12432d97d61b7af51
Reviewed-on: https://gerrit.libreoffice.org/24604Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Jenkins <ci@libreoffice.org>