Bugfixes and refactoring for SLA backend

remove duplicate code


Mark conversion constructors of EigenMesh3D `explicit`


Working on mesh simplification for hollowed interior


Fix bug SPE-1074: crash with empty supports and disabled pad.


fix regression after refactor


Remove unfinished code


Fix missing includes and dumb comments

src/libslic3r/SLAPrint.cpp

@@ -1095,8 +1095,6 @@ const ExPolygons &SliceRecord::get_slice(SliceOrigin o) const
     const std::vector<ExPolygons>& v = o == soModel? m_po->get_model_slices() :
                                                      m_po->get_support_slices();
 
-    if(idx >= v.size()) return EMPTY_SLICE;
-
     return idx >= v.size() ? EMPTY_SLICE : v[idx];
 }