Fix a crash when live view is not supported ...

... and live view is switched on and off again
graduatednd: fix (marginal) bug in distance calculation
Merge branch 'master' of ssh://github.com/darktable-org/darktable
Merge branch 'master' into gtk3-00-use-_key_-infix

* master:
  graduatednd: fix (marginal) bug in distance calculation
  Fix a crash when live view is not supported ...