router: fix use-after-free error when dragging a single (no tracks attached via) in shove mode

Fixes: https://gitlab.com/kicad/code/kicad/-/work_items/23449

(cherry picked from commit 1909f3a8b3)

pcbnew/router/pns_shove.cpp

@@ -2443,29 +2443,13 @@ SHOVE::SHOVE_STATUS SHOVE::Run()
     m_currentNode = parent->Branch();
     m_currentNode->ClearRanks();
 
-
-
-
-
-
     //nodeStats( Dbg(), m_currentNode, "right-after-branch" );
 
     auto iface = Router()->GetInterface();
 
-    //    for ( auto& hq : m_headLines )
-    //      if( hq.oldHead )
-    //        m_currentNode->Remove( *hq.oldHead );
-
-
     // Push the via to its new location
     for( auto& headLineEntry : m_headLines )
     {
-        //if( rootEntry->line ) // head already processed in previous steps
-        //{
-        //  PNS_DBG( Dbg(), Message, wxString::Format( "RL found" ) );
-
-        //continue;
-        //}
         m_currentNode->ClearRanks();
 
         if( headLineEntry.theVia )
@@ -2619,6 +2603,11 @@ SHOVE::SHOVE_STATUS SHOVE::Run()
             }
         }
 
+	// NODE's destructor invalidates all linked items in the LINEs stored in the stack/queue
+	// Erase them first to avoid a use-after-free issue.
+        m_lineStack.clear();
+        m_optimizerQueue.clear();
+
         pruneRootLines( m_currentNode );
 
         delete m_currentNode;