Fix debug assertion in Altium and CADSTAR schematic importers.

eeschema/sch_plugins/altium/sch_altium_plugin.cpp

@@ -177,6 +177,8 @@ SCH_SHEET* SCH_ALTIUM_PLUGIN::Load( const wxString& aFileName, SCHEMATIC* aSchem
         m_rootSheet = new SCH_SHEET( aSchematic );
         m_rootSheet->SetFileName( fileName.GetFullPath() );
 
+        aSchematic->SetRoot( m_rootSheet );
+
         SCH_SHEET_PATH sheetpath;
         sheetpath.push_back( m_rootSheet );
 

eeschema/sch_plugins/cadstar/cadstar_sch_archive_loader.cpp

@@ -103,25 +103,25 @@ void CADSTAR_SCH_ARCHIVE_LOADER::Load( SCHEMATIC* aSchematic, SCH_SHEET* aRootSh
 
     loadTextVariables(); // Load text variables right at the start to ensure bounding box
                          // calculations work correctly for text items
-        checkPoint(); // Step 1
+    checkPoint(); // Step 1
     loadSheets();
-        checkPoint(); // Step 2
+    checkPoint(); // Step 2
     loadHierarchicalSheetPins();
-        checkPoint(); // Step 3
+    checkPoint(); // Step 3
     loadPartsLibrary();
-        checkPoint(); // Step 4, Subdivided into extra steps
+    checkPoint(); // Step 4, Subdivided into extra steps
     loadSchematicSymbolInstances();
-        checkPoint(); // Step 5
+    checkPoint(); // Step 5
     loadBusses();
-        checkPoint(); // Step 6
+    checkPoint(); // Step 6
     loadNets();
-        checkPoint(); // Step 7
+    checkPoint(); // Step 7
     loadFigures();
-        checkPoint(); // Step 8
+    checkPoint(); // Step 8
     loadTexts();
-        checkPoint(); // Step 9
+    checkPoint(); // Step 9
     loadDocumentationSymbols();
-        checkPoint(); // Step 10
+    checkPoint(); // Step 10
 
     if( Schematic.VariantHierarchy.Variants.size() > 0 )
     {

eeschema/sch_plugins/cadstar/cadstar_sch_archive_plugin.cpp

@@ -2,7 +2,7 @@
  * This program source code file is part of KiCad, a free EDA CAD application.
  *
  * Copyright (C) 2020 Roberto Fernandez Bautista <roberto.fer.bau@gmail.com>
- * Copyright (C) 2020 KiCad Developers, see AUTHORS.txt for contributors.
+ * Copyright (C) 2020-2021 KiCad Developers, see AUTHORS.txt for contributors.
  *
  * This program is free software: you can redistribute it and/or modify it
  * under the terms of the GNU General Public License as published by the
@@ -75,6 +75,7 @@ SCH_SHEET* CADSTAR_SCH_ARCHIVE_PLUGIN::Load( const wxString& aFileName, SCHEMATI
     {
         rootSheet = new SCH_SHEET( aSchematic );
         rootSheet->SetFileName( aFileName );
+        aSchematic->SetRoot( rootSheet );
     }