[modules] Fix crash when writing an update record for a redeclaration of an empty namespace.

llvm-svn: 241732
diff --git a/clang/test/Modules/Inputs/namespaces-left.h b/clang/test/Modules/Inputs/namespaces-left.h
index 787fe75..5badf62 100644
--- a/clang/test/Modules/Inputs/namespaces-left.h
+++ b/clang/test/Modules/Inputs/namespaces-left.h
@@ -71,3 +71,5 @@
   }
   Foo *getFoo();
 }
+
+namespace Empty {}