Fix an issue when using the widget with a far camera position

When we want to interact with each point handlers of the vtkLineSource, if the camera are far away we can't interact with theses widgets correctly.

Seems to be a side effect of the invert case, when we are in extreme zoom (see this MR). To be sure that we can handle this 2 cases, we detect if the cursor is near of the widget by comparing their positions in screen space and not in world space.