Fix #35683: Addon working fine in console. But crashed when click GUI button.

Crash happened in ED_view3d_calc_zfac and happend in cases operator was invoked
from a region different from RGN_TYPE_WINDOW.

For a transformation zfac is only used in convertViewVec in cases region is
RGN_TYPE_WINDOW, so solved by just adding extra check in calculateCenter
for this particular case.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57336 954f8c5b-7b00-dc11-b283-0030488c597c
Made blender compilable with strict flags again.

Maybe Joshua would want to check on arguments for nlaevalchan_verify.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@57337 954f8c5b-7b00-dc11-b283-0030488c597c