Fix "argument of type 'NoneType' is not iterable" error in de page "B…

…auerngabel"

This is a chess board table and it doesn't have `class` attribute.

Since this `if` branch is not implemented, I'll omit the test for this
error.

src/wiktextract/extractor/de/page.py

@@ -224,7 +224,7 @@ def process_pos_section(
         elif (
             isinstance(non_l4_node, WikiNode)
             and non_l4_node.kind == NodeKind.TABLE
-            and "inflection-table" in non_l4_node.attrs.get("class")
+            and "inflection-table" in non_l4_node.attrs.get("class", "")
         ):
             # XXX: de: Extract html form table
             pass