Fix autoslice check so it doesn't slice if there is no need

CURA-5130

plugins/CuraEngineBackend/CuraEngineBackend.py

@@ -119,6 +119,7 @@ class CuraEngineBackend(QObject, Backend):
         self._postponed_scene_change_sources = []  # scene change is postponed (by a tool)
 
         self._slice_start_time = None
+        self._is_disabled = False
 
         Preferences.getInstance().addPreference("general/auto_slice", True)
 
@@ -405,6 +406,7 @@ class CuraEngineBackend(QObject, Backend):
     #   - decorator isBlockSlicing is found (used in g-code reader)
     def determineAutoSlicing(self):
         enable_timer = True
+        self._is_disabled = False
 
         if not Preferences.getInstance().getValue("general/auto_slice"):
             enable_timer = False
@@ -412,6 +414,7 @@ class CuraEngineBackend(QObject, Backend):
             if node.callDecoration("isBlockSlicing"):
                 enable_timer = False
                 self.backendStateChange.emit(BackendState.Disabled)
+                self._is_disabled = True
             gcode_list = node.callDecoration("getGCodeList")
             if gcode_list is not None:
                 self._scene.gcode_dict[node.callDecoration("getBuildPlateNumber")] = gcode_list
@@ -524,6 +527,9 @@ class CuraEngineBackend(QObject, Backend):
 
     ##  Convenient function: mark everything to slice, emit state and clear layer data
     def needsSlicing(self):
+        self.determineAutoSlicing()
+        if self._is_disabled:
+            return
         self.stopSlicing()
         self.markSliceAll()
         self.processingProgress.emit(0.0)