FDO#74774 : issue with number of child nodes of tag CubicBezierTo.

Issue :
 - Number of child nodes required by cubicBexTo should be 3 of type "pt".
   While exporting, sometimes the child nodes are less than 3.
   The sequence of writing these tags was getting messed up.

Implementation :
 - corrected the logic for writing the sequence of cubicBexTo tag.

Change-Id: Ic26db72b2c516276c2e6452a21b4106d6a0a1a80
Reviewed-on: https://gerrit.libreoffice.org/7990
Reviewed-by: Miklos Vajna <vmiklos@collabora.co.uk>
Tested-by: Miklos Vajna <vmiklos@collabora.co.uk>