bpo-35742: Fix test_envar_unimportable in test_builtin. (GH-11561)


Handle the case of an empty module name in PYTHONBREAKPOINT.

Fixes a regression introduced in bpo-34756.
(cherry picked from commit 3607ef43c4a1a24d44f39ff54a77fc0af5bfa09a)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>
diff --git a/Lib/test/test_builtin.py b/Lib/test/test_builtin.py
index 7c9768a..c3f04ec 100644
--- a/Lib/test/test_builtin.py
+++ b/Lib/test/test_builtin.py
@@ -1601,6 +1601,7 @@
     def test_envar_unimportable(self):
         for envar in (
                 '.', '..', '.foo', 'foo.', '.int', 'int.',
+                '.foo.bar', '..foo.bar', '/./',
                 'nosuchbuiltin',
                 'nosuchmodule.nosuchcallable',
                 ):