Pressing Ctrl+R when blender was built without bullet would crash.
- add checks so rigid-body operators only return FINISHED when they make some changes to the scene.
- remove (scene == NULL) checks, poll already catches these.


git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55916 954f8c5b-7b00-dc11-b283-0030488c597c