Camera tracking, minor changes:

- Fill in image dimension for camera intrinsics used for
  solution refirement.
- Retrieve K3 from camera intrinsics after refining.

Shall be no functional changes, just makes things clear
and robust for further improvements.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54845 954f8c5b-7b00-dc11-b283-0030488c597c