GerbView: only erase current layer if a new file is chosen

gerbview/files.cpp

@@ -110,7 +110,6 @@ void GERBVIEW_FRAME::Files_io( wxCommandEvent& event )
     switch( id )
     {
     case wxID_FILE:
-        Erase_Current_DrawLayer( false );
         LoadGerberFiles( wxEmptyString );
         break;
 
@@ -215,6 +214,8 @@ bool GERBVIEW_FRAME::LoadGerberFiles( const wxString& aFullFileName )
         m_mruPath = currentPath = filename.GetPath();
     }
 
+    Erase_Current_DrawLayer( false );
+
     // Set the busy cursor
     wxBusyCursor wait;