Fix small bug when updating projects from rev. 9 to 10

When two Specular BTDFs were almost paired but not quite (because the IORs wouldn't match, for instance) then both were inserted into the assembly but potentially with the same name.

When this happens, we now skip the insertion of the second one.

src/appleseed/renderer/modeling/project/projectfileupdater.cpp

@@ -864,10 +864,15 @@ namespace
                         // Extract mat1 from the assembly.
                         auto_release_ptr<Material> mat1_owner = assembly.materials().remove(mat1.m_material);
 
+                        // Extract mat1's BSDF from the assembly.
+                        auto_release_ptr<BSDF> bsdf_owner = assembly.bsdfs().remove(mat1.m_bsdf);
+
                         // Update mat1's BSDF.
                         // todo: make sure the BSDF is not used in another material.
-                        auto_release_ptr<BSDF> bsdf_owner = assembly.bsdfs().remove(mat1.m_bsdf);
                         update_bsdf(mat1);
+                        assert(assembly.bsdfs().get_by_name(bsdf_owner->get_name()) == nullptr);
+
+                        // Insert mat1's BSDF back into the assembly.
                         assembly.bsdfs().insert(bsdf_owner);
 
                         // Rename mat1.
@@ -897,11 +902,16 @@ namespace
 
                 if (!i->m_updated)
                 {
+                    // Extract the material's BSDF from the assembly.
+                    auto_release_ptr<BSDF> bsdf_owner = assembly.bsdfs().remove(i->m_bsdf);
+
                     // Update the material's BSDF.
                     // todo: make sure the BSDF is not used in another material.
-                    auto_release_ptr<BSDF> bsdf_owner = assembly.bsdfs().remove(i->m_bsdf);
                     update_bsdf(*i);
-                    assembly.bsdfs().insert(bsdf_owner);
+
+                    // Insert the material's BSDF back into the assembly.
+                    if (assembly.bsdfs().get_by_name(bsdf_owner->get_name()) == nullptr)
+                        assembly.bsdfs().insert(bsdf_owner);
 
                     i->m_updated = true;
                 }