fix: reindex_studio could crash if an XBlock child isn't loadable (#37177)

Co-authored-by: Chris Chávez <xnpiochv@gmail.com>

Author: bradenmacdonald

openedx/core/djangoapps/content/search/api.py

@@ -40,6 +40,7 @@
 from openedx.core.djangoapps.content.search.models import IncrementalIndexCompleted, get_access_ids_for_request
 from openedx.core.djangoapps.content_libraries import api as lib_api
 from xmodule.modulestore.django import modulestore
+from xmodule.modulestore.exceptions import ItemNotFoundError
 
 from .documents import (
     Fields,
@@ -278,6 +279,9 @@ def _recurse_children(block, fn, status_cb: Callable[[str], None] | None = None)
         for child_id in block.children:
             try:
                 child = block.get_child(child_id)
+                if child is None:
+                    # XBlocks with XModuleMixin will return None from get_child() instead of raising an exception :/
+                    raise ItemNotFoundError(f"block.get_child() from {block.usage_key} failed to load child {child_id}")
             except Exception as err:  # pylint: disable=broad-except
                 log.exception(err)
                 if status_cb is not None: