glTF exporter: fix to generate valid file when zero-weight verts

A better fix will come later

io_scene_gltf2/__init__.py

@@ -15,7 +15,7 @@
 bl_info = {
     'name': 'glTF 2.0 format',
     'author': 'Julien Duroure, Scurest, Norbert Nopper, Urs Hanselmann, Moritz Becher, Benjamin Schmithüsen, Jim Eckerlein, and many external contributors',
-    "version": (1, 3, 46),
+    "version": (1, 3, 47),
     'blender': (2, 90, 0),
     'location': 'File > Import-Export',
     'description': 'Import-Export as glTF 2.0',

io_scene_gltf2/blender/exp/gltf2_blender_extract.py

@@ -286,6 +286,7 @@ def extract_primitives(glTF, blender_mesh, library, blender_object, blender_vert
                         bones.append((joint, weight))
                 bones.sort(key=lambda x: x[1], reverse=True)
                 bones = tuple(bones)
+                if not bones: bones = ((0, 1.0),)  # HACK for verts with zero weight (#308)
                 vert += (bones,)
 
             for shape_key in shape_keys: