Refuse to drill a broken mesh

Hole parameters defaults and limits changed a bit

src/slic3r/GUI/Gizmos/GLGizmoHollow.hpp

@@ -58,7 +58,7 @@ private:
 
     bool  m_show_supports = true;
     float m_new_hole_radius = 2.f;        // Size of a new hole.
-    float m_new_hole_height = 5.f;
+    float m_new_hole_height = 6.f;
     mutable std::vector<bool> m_selected; // which holes are currently selected
 
     bool m_enable_hollowing = true;