fix for various crashes from incorrect poll functions.
- bevel had incorrect cancel when initialization failed which could crash (own mistake).
- main particle poll function didnt check if the area/region were NULL.
- some uv operators needed space image but didnt check for it. also use uv_ prefix for most operator functions.

git-svn-id: https://svn.blender.org/svnroot/bf-blender/trunk/blender@55900 954f8c5b-7b00-dc11-b283-0030488c597c