Fix checking if container stack exists

It was checking a container stack ID against the definition containers, which doesn't match.

Contributes to issue CURA-3973.

cura/Settings/MachineManager.py

@@ -91,7 +91,7 @@ class MachineManager(QObject):
         self._printer_output_devices = []
         Application.getInstance().getOutputDeviceManager().outputDevicesChanged.connect(self._onOutputDevicesChanged)
 
-        if active_machine_id != "" and ContainerRegistry.getInstance().findDefinitionContainers(id = active_machine_id):
+        if active_machine_id != "" and ContainerRegistry.getInstance().findContainerStacks(id = active_machine_id):
             # An active machine was saved, so restore it.
             self.setActiveMachine(active_machine_id)
             if self._global_container_stack and self._global_container_stack.getProperty("machine_extruder_count", "value") > 1: