Fixed crash when no transformation was provided in 3mf file

plugins/3MFReader/ThreeMFReader.py

@@ -50,6 +50,7 @@ class ThreeMFReader(MeshReader):
                     node.setSelectable(True)
                     # Magical python comprehension; looks for the matching transformation
                     transformation = next((x for x in root.model.build.item if x["objectid"] == object["id"]), None)
+                    if transformation["transform"]:
                         splitted_transformation = transformation["transform"].split()
                         
                         ## Transformation is saved as:
@@ -95,9 +96,12 @@ class ThreeMFReader(MeshReader):
                     result.addChild(node)
                 
                 #  If there is more then one object, group them.
+                try:
                     if len(root.model.resources.object) > 1:  
                         group_decorator = GroupDecorator()
                         result.addDecorator(group_decorator)
+                except:
+                    pass
             except Exception as e:
                 print("EXCEPTION: " ,e)      
         return result