Fix #34009: multi user curves + deform modifier behavior

Issue was caused by storing BB calculated from final displist in
Curve datablock and not having Object's BB at all. This is not
clear at how could have been worked for so long.

Changed it so Curve's BB is calculated from non-deformed displist,
which matches BKE_object_min_max and BKE_curve_texspace_calc and
made it so Object's BB would be calculated from final displist.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@54181 954f8c5b-7b00-dc11-b283-0030488c597c