Don't access tools after they've shut down.

eeschema/sch_edit_frame.cpp

@@ -308,13 +308,18 @@ SCH_EDIT_FRAME::~SCH_EDIT_FRAME()
 {
     // Shutdown all running tools
     if( m_toolManager )
+    {
         m_toolManager->ShutdownAllTools();
+        delete m_toolManager;
+        m_toolManager = nullptr;
+    }
 
     delete m_item_to_repeat;        // we own the cloned object, see this->SaveCopyForRepeatItem()
 
     SetScreen( NULL );
 
     delete m_schematic;
+    m_schematic = nullptr;
 
     // Close the project if we are standalone, so it gets cleaned up properly
     if( Kiface().IsSingle() )