3d viewer fix for 3d single material object Diffuse Only opacity

3d-viewer/3d_rendering/legacy/3d_model.cpp

@@ -149,7 +149,8 @@ MODEL_3D::MODEL_3D( const S3DMODEL& a3DModel, MATERIAL_MODE aMaterialMode )
         auto& mesh_group = mesh_groups[mesh.m_MaterialIdx];
         auto& material = m_materials[mesh.m_MaterialIdx];
 
-        if( material.IsTransparent() )
+        if( material.IsTransparent()
+                && m_materialMode != MATERIAL_MODE::DIFFUSE_ONLY )
             m_have_transparent_meshes = true;
          else
             m_have_opaque_meshes = true;