Keep previous systems in plotting entries

SpanshRouter/SpanshRouter.py

@@ -144,7 +144,9 @@ class SpanshRouter():
             self.show_route_gui(False)
 
         else:
+            if len(self.source_ac.var.get()) == 0:
                 self.source_ac.put_placeholder()
+            if len(self.dest_ac.var.get()) == 0:
                 self.dest_ac.put_placeholder()
             self.source_ac.grid_remove()
             self.dest_ac.grid_remove()