If mpGraphics is set, then return true as initialization of graphics
device has already been done. I've also removed unnecessary variables
which were a left over from the function splits.

Change-Id: I25c25b93b9db2c112c9a1aea278b1ec3e0590303
Reviewed-on: https://gerrit.libreoffice.org/8581Reviewed-by: Michael Meeks <michael.meeks@collabora.com>
Tested-by: Michael Meeks <michael.meeks@collabora.com>