PNS router: reset forced cursor position

Track dragging forces the cursor position, which is still kept when PNS
router is launched again. It is avoided by resetting the force cursor
position option before running the event loop.

pcbnew/router/router_tool.cpp

@@ -859,9 +859,10 @@ int ROUTER_TOOL::mainLoop( PNS::ROUTER_MODE aMode )
 
     m_router->SetMode( aMode );
 
-    controls()->ShowCursor( true );
-
-    m_startSnapPoint = getViewControls()->GetCursorPosition();
+    VIEW_CONTROLS* ctls = getViewControls();
+    ctls->ShowCursor( true );
+    ctls->ForceCursorPosition( false );
+    m_startSnapPoint = ctls->GetCursorPosition();
 
     std::unique_ptr<ROUTER_TOOL_MENU> ctxMenu( new ROUTER_TOOL_MENU( board, *frame, aMode ) );
     SetContextMenu( ctxMenu.get() );