Fixed crash where collection children are ID blocks instead of GR blocks

Not sure when/how that happens, but it happened on a lighting file of the
Spring project, when linking in a nested collection of which parts where
also linked in from other blend files.

blender_asset_tracer/blendfile/__init__.py

@@ -498,9 +498,13 @@ class BlendFileBlock:
     def dna_type(self) -> dna.Struct:
         return self.bfile.structs[self.sdna_index]
 
+    @property
+    def dna_type_id(self) -> bytes:
+        return self.dna_type.dna_type_id
+
     @property
     def dna_type_name(self) -> str:
-        return self.dna_type.dna_type_id.decode('ascii')
+        return self.dna_type_id.decode('ascii')
 
     @property
     def id_name(self) -> typing.Optional[bytes]:

blender_asset_tracer/trace/expanders.py

@@ -123,7 +123,7 @@ def _expand_curve(block: blendfile.BlendFileBlock):
 
 @dna_code('GR')
 def _expand_group(block: blendfile.BlendFileBlock):
-    log.debug('Block: %s', block)
+    log.debug('Collection/group Block: %s (name=%s)', block, block.id_name)
 
     objects = block.get_pointer((b'gobject', b'first'))
     for item in iterators.listbase(objects):
@@ -140,7 +140,15 @@ def _expand_group(block: blendfile.BlendFileBlock):
             subcoll = child.get_pointer(b'collection')
             if subcoll is None:
                 continue
-            log.debug('recursing into child collection %s', subcoll.id_name)
+
+            if subcoll.dna_type_id == b'ID':
+                # No idea when this happens, but it happened in the Chimes
+                # set of the Spring project. This fixed it.
+                yield subcoll
+                continue
+
+            log.debug('recursing into child collection %s (name=%r, type=%r)',
+                      subcoll, subcoll.id_name, subcoll.dna_type_name)
             yield from _expand_group(subcoll)