BUG: Fix crash for invalid model input
BUG: Fix crash for invalid model input

When input model was too heavily decimated then subdivision failed and a GetPoint(-1) call crashed the application.
Fixed this by skipping subdivision if it is not successful.

Additional fixes:
- Fixed openSurfaceAtPoint method. As a result, now centerline starts from the seed point position.
- Improved error reporting (exception text is now displayed in a popup window).

vmtk/SlicerExtension-VMTK