bug with crash, maybe hidden faces or normals

[micheus]

I just fixed it. I should be applied to the next release of Wings3D.

By now, if you want (and know hot to) update the files you can find them here
- wings_tweak.beam (C:\Program Files\wings3d_1.5.2\lib\wings-1.5.2\ebin)
- wpc_sculpt.beam (C:\Program Files\wings3d_1.5.2\lib\wings-1.5.2\plugins\commands)