Reduce nesting complexity with some pre-checks

There were two pre-checks here, where the main body of the function was indented two deep. Instead, just early-out if the checks fail. This is easier to read and understand.

Found during investigation of CURA-8128.

plugins/PerObjectSettingsTool/PerObjectSettingVisibilityHandler.py

@@ -73,38 +73,40 @@ class PerObjectSettingVisibilityHandler(UM.Settings.Models.SettingVisibilityHand
 
         # Add all instances that are not added, but are in visibility list
         for item in visible:
-            if settings.getInstance(item) is None:  # Setting was not added already.
-                definition = self._stack.getSettingDefinition(item)
-                if definition:
-                    new_instance = SettingInstance(definition, settings)
+            if settings.getInstance(item) is not None:  # Setting was added already.
+                continue
+            definition = self._stack.getSettingDefinition(item)
+            if not definition:
+                Logger.log("w", f"Unable to add instance ({item}) to per-object visibility because we couldn't find the matching definition.")
+                continue
+
+            new_instance = SettingInstance(definition, settings)
+            stack_nr = -1
+            stack = None
+            # Check from what stack we should copy the raw property of the setting from.
+            if self._stack.getProperty("machine_extruder_count", "value") > 1:
+                if definition.limit_to_extruder != "-1":
+                    # A limit to extruder function was set and it's a multi extrusion machine. Check what stack we do need to use.
+                    stack_nr = str(int(round(float(self._stack.getProperty(item, "limit_to_extruder")))))
+
+                # Check if the found stack_number is in the extruder list of extruders.
+                if stack_nr not in ExtruderManager.getInstance().extruderIds and self._stack.getProperty("extruder_nr", "value") is not None:
                     stack_nr = -1
-                    stack = None
-                    # Check from what stack we should copy the raw property of the setting from.
-                    if self._stack.getProperty("machine_extruder_count", "value") > 1:
-                        if definition.limit_to_extruder != "-1":
-                            # A limit to extruder function was set and it's a multi extrusion machine. Check what stack we do need to use.
-                            stack_nr = str(int(round(float(self._stack.getProperty(item, "limit_to_extruder")))))
-
-                        # Check if the found stack_number is in the extruder list of extruders.
-                        if stack_nr not in ExtruderManager.getInstance().extruderIds and self._stack.getProperty("extruder_nr", "value") is not None:
-                            stack_nr = -1
-
-                        # Use the found stack number to get the right stack to copy the value from.
-                        if stack_nr in ExtruderManager.getInstance().extruderIds:
-                            stack = ContainerRegistry.getInstance().findContainerStacks(id = ExtruderManager.getInstance().extruderIds[stack_nr])[0]
-                    else:
-                        stack = self._stack
-
-                    # Use the raw property to set the value (so the inheritance doesn't break)
-                    if stack is not None:
-                        new_instance.setProperty("value", stack.getRawProperty(item, "value"))
-                    else:
-                        new_instance.setProperty("value", None)
-                    new_instance.resetState()  # Ensure that the state is not seen as a user state.
-                    settings.addInstance(new_instance)
-                    visibility_changed = True
-                else:
-                    Logger.log("w", "Unable to add instance (%s) to per-object visibility because we couldn't find the matching definition", item)
+
+                # Use the found stack number to get the right stack to copy the value from.
+                if stack_nr in ExtruderManager.getInstance().extruderIds:
+                    stack = ContainerRegistry.getInstance().findContainerStacks(id = ExtruderManager.getInstance().extruderIds[stack_nr])[0]
+            else:
+                stack = self._stack
+
+            # Use the raw property to set the value (so the inheritance doesn't break)
+            if stack is not None:
+                new_instance.setProperty("value", stack.getRawProperty(item, "value"))
+            else:
+                new_instance.setProperty("value", None)
+            new_instance.resetState()  # Ensure that the state is not seen as a user state.
+            settings.addInstance(new_instance)
+            visibility_changed = True
 
         if visibility_changed:
             self.visibilityChanged.emit()