Fix issue packing lamps with non-IES 'storage'

Lamp/light nodes might have a `storage` property that might point to an
IES texture node (which has the expected `filepath`), but not always.
The latter now no longer crashes BAT.

This fixes https://projects.blender.org/blender/blender-asset-tracer/pulls/92883

blender_asset_tracer/trace/blocks2assets.py

@@ -226,5 +226,11 @@ def lamp(block: blendfile.BlendFileBlock) -> typing.Iterator[result.BlockUsage]:
         storage = node.get_pointer(b"storage")
         if not storage:
             continue
-        path, field = storage.get(b"filepath", return_field=True)
+
+        # A storage block of `NodeShaderTexIES` type has a `filepath`, but not
+        # all types that can be pointed to by the `storage` pointer do.
+        path, field = storage.get(b"filepath", return_field=True, default=None)
+        if path is None:
+            continue
+
         yield result.BlockUsage(block, path, path_full_field=field)