glTF exporter: fix some strange reference error in blender api when exporting shapekeys / ApplyModifier

Referenced by issue blender/blender#74274, Blender 2.82a proposed revisions

io_scene_gltf2/__init__.py

@@ -15,7 +15,7 @@
 bl_info = {
     'name': 'glTF 2.0 format',
     'author': 'Julien Duroure, Norbert Nopper, Urs Hanselmann, Moritz Becher, Benjamin Schmithüsen, Jim Eckerlein, and many external contributors',
-    "version": (1, 2, 19),
+    "version": (1, 2, 20),
     'blender': (2, 81, 6),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/exp/gltf2_blender_gather_mesh.py

@@ -135,6 +135,14 @@ def __gather_weights(blender_mesh: bpy.types.Mesh,
                      export_settings
                      ) -> Optional[List[float]]:
 
+    # Seems that in some files, when using Apply Modifier, shape_keys return an error
+    # ReferenceError: StructRNA of type Mesh has been removed
+    # Because shapekeys are not exported in that case, we can return None
+    try:
+        blender_mesh.shape_keys
+    except:
+        return None
+
     if not export_settings[MORPH] or not blender_mesh.shape_keys:
         return None