Import: morph target named 'Basis' imported wrong
Since we use 'Basis' as the name of the special first shape key, we shouldn't let morph targets use it. You can test by taking, say, MorphStressTest, and renaming one of targetNames in the glTF to 'Basis'.

Fix is just to use `set(['Basis'])` [here](https://github.com/KhronosGroup/glTF-Blender-IO/blob/bb488b245f0c83fdd566b43c2c762d469c044326/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py#L168), so 'Basis' will always be regarded as "taken".
diff --git a/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py b/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py
index 48f18079..92f8f469 100755
--- a/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py
+++ b/addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py
@@ -165,7 +165,7 @@ class BlenderGlTF():
         # Calculate names for each mesh's shapekeys
         for mesh in gltf.data.meshes or []:
             mesh.shapekey_names = []
-            used_names = set()
+            used_names = set(['Basis']) #Be sure to not use 'Basis' name at import, this is a reserved name
 
             # Some invalid glTF files has empty primitive tab
             if len(mesh.primitives) > 0:
['addons/io_scene_gltf2/blender/imp/gltf2_blender_gltf.py']