Prevent crashes when a variant could not be found

This should not happen, but we've seen some cases where it would cause a crash, usually
when a previous upgrade did something a bit weird (in this specific case; a printer
with an empty variant, whereas it should have a variant).

Since any change that the user will make will ensure that the variant is no longer empty (eg;
any selection of a variant will mean it's no longer empty) and that there is no way back,
it should be pretty safe to ignore the situation as it will resolve itself eventually

CURA-6992

cura/Machines/Models/IntentModel.py

@@ -7,6 +7,7 @@ from PyQt5.QtCore import Qt, QObject, pyqtProperty, pyqtSignal
 import cura.CuraApplication
 from UM.Qt.ListModel import ListModel
 from UM.Settings.ContainerRegistry import ContainerRegistry
+from UM.Logger import Logger
 from cura.Machines.ContainerTree import ContainerTree
 from cura.Machines.MaterialNode import MaterialNode
 from cura.Machines.Models.MachineModelUtils import fetchLayerHeight
@@ -101,6 +102,9 @@ class IntentModel(ListModel):
 
         for extruder in global_stack.extruderList:
             active_variant_name = extruder.variant.getMetaDataEntry("name")
+            if active_variant_name not in machine_node.variants:
+                Logger.log("w", "Could not find the variant %s", active_variant_name)
+                continue
             active_variant_node = machine_node.variants[active_variant_name]
             active_material_node = active_variant_node.materials[extruder.material.getMetaDataEntry("base_file")]
             nodes.add(active_material_node)

cura/Settings/IntentManager.py

@@ -39,7 +39,11 @@ class IntentManager(QObject):
     #   an empty list if nothing was found.
     def intentMetadatas(self, definition_id: str, nozzle_name: str, material_base_file: str) -> List[Dict[str, Any]]:
         intent_metadatas = []  # type: List[Dict[str, Any]]
+        try:
             materials = ContainerTree.getInstance().machines[definition_id].variants[nozzle_name].materials
+        except KeyError:
+            Logger.log("w", "Unable to find the machine %s or the variant %s", definition_id, nozzle_name)
+            materials = {}
         if material_base_file not in materials:
             return intent_metadatas