Add sheetpath instances when importing sheets from Altium.

eeschema/sch_plugins/altium/sch_altium_plugin.cpp

@@ -179,6 +179,13 @@ SCH_SHEET* SCH_ALTIUM_PLUGIN::Load( const wxString& aFileName, SCHEMATIC* aSchem
     {
         m_rootSheet = new SCH_SHEET( aSchematic );
         m_rootSheet->SetFileName( fileName.GetFullPath() );
+
+        SCH_SHEET_PATH sheetpath;
+        sheetpath.push_back( m_rootSheet );
+
+        m_rootSheet->AddInstance( sheetpath.Path() );
+        m_rootSheet->SetPageNumber( sheetpath, "#" );   // We'll update later if we find a
+                                                        // pageNumber record for it
     }
 
     if( !m_rootSheet->GetScreen() )
@@ -1447,6 +1454,14 @@ void SCH_ALTIUM_PLUGIN::ParseSheetSymbol( int aIndex, const std::map<wxString,
     sheet->SetFlags( IS_NEW );
     m_currentSheet->GetScreen()->Append( sheet );
 
+    SCH_SHEET_PATH sheetpath;
+    m_rootSheet->LocatePathOfScreen( m_currentSheet->GetScreen(), &sheetpath );
+    sheetpath.push_back( sheet );
+
+    sheet->AddInstance( sheetpath.Path() );
+    sheet->SetPageNumber( sheetpath, "#" );   // We'll update later if we find a pageNumber
+                                              // record for it
+
     m_sheets.insert( { aIndex, sheet } );
 }