In Submodule.iter_items, don't attach second empty iterator

This fixes the minor bug where a separate empty iterator was bound
to the StopIteration exception raised as a result of returning from
the generator function (gitpython-developers#1779).

This change does not cause what exceptions are raised from
GitPython code in any situations, nor how many items any iterators
yield.

Author: EliahKagan

Diff for: git/objects/submodule/base.py

@@ -1401,7 +1401,7 @@ def iter_items(
             pc = repo.commit(parent_commit)  # Parent commit instance
             parser = cls._config_parser(repo, pc, read_only=True)
         except (IOError, BadName):
-            return iter([])
+            return
         # END handle empty iterator
 
         for sms in parser.sections():