Fix pcbnew: refresh canvas on opening a file only after mouse move

Fixes: lp:1760819
* https://bugs.launchpad.net/kicad/+bug/1760819

pcbnew/pcb_edit_frame.cpp

@@ -966,6 +966,8 @@ void PCB_EDIT_FRAME::onBoardLoaded()
     // Display the loaded board:
     Zoom_Automatique( false );
 
+    Refresh();
+
     SetMsgPanel( GetBoard() );
     SetStatusText( wxEmptyString );
 }