Added header guards to files in directories avmedia/, basegfx/, chart2/, and
connectivity/

Change-Id: I94ec438ec918ccef1c518edfd9ab4944e9e2961b
Reviewed-on: https://gerrit.libreoffice.org/9555Reviewed-by: Noel Grandin <noelgrandin@gmail.com>
Tested-by: Noel Grandin <noelgrandin@gmail.com>