Be a bit more gracefull when adding a machine failed

This seems to happen for people that manually add machines to cura
but mess something up when copying the files.

CURA-3X

cura/Settings/CuraStackBuilder.py

@@ -58,7 +58,10 @@ class CuraStackBuilder:
         # Create ExtruderStacks
         extruder_dict = machine_definition.getMetaDataEntry("machine_extruder_trains")
         for position in extruder_dict:
+            try:
                 cls.createExtruderStackWithDefaultSetup(new_global_stack, position)
+            except IndexError:
+                return None
 
         for new_extruder in new_global_stack.extruders.values():  # Only register the extruders if we're sure that all of them are correct.
             registry.addContainer(new_extruder)

cura/Settings/MachineManager.py

@@ -347,9 +347,9 @@ class MachineManager(QObject):
                 return cast(GlobalStack, machine)
         return None
 
-    @pyqtSlot(str)
-    @pyqtSlot(str, str)
-    def addMachine(self, definition_id: str, name: Optional[str] = None) -> None:
+    @pyqtSlot(str, result=bool)
+    @pyqtSlot(str, str, result = bool)
+    def addMachine(self, definition_id: str, name: Optional[str] = None) -> bool:
         Logger.log("i", "Trying to add a machine with the definition id [%s]", definition_id)
         if name is None:
             definitions = CuraContainerRegistry.getInstance().findDefinitionContainers(id = definition_id)
@@ -364,6 +364,8 @@ class MachineManager(QObject):
             self.setActiveMachine(new_stack.getId())
         else:
             Logger.log("w", "Failed creating a new machine!")
+            return False
+        return True
 
     def _checkStacksHaveErrors(self) -> bool:
         time_start = time.time()

resources/qml/WelcomePages/AddNetworkOrLocalPrinterContent.qml

@@ -151,10 +151,11 @@ Item
                 // Create a local printer
                 const localPrinterItem = addLocalPrinterDropDown.contentItem.currentItem
                 const printerName = addLocalPrinterDropDown.contentItem.printerName
-                Cura.MachineManager.addMachine(localPrinterItem.id, printerName)
-
+                if(Cura.MachineManager.addMachine(localPrinterItem.id, printerName))
+                {
                     base.showNextPage()
                 }
             }
         }
+    }
 }