#6373: SystemError in str.encode('latin1', 'surrogateescape')

if the string contains unpaired surrogates.
(In debug build, crash in assert())

This can happen with normal processing, if python starts with utf-8,
then calls sys.setfilesystemencoding('latin-1')

Lib/test/test_codecs.py

@@ -1549,6 +1549,11 @@ class SurrogateEscapeTest(unittest.TestCase):
         self.assertEqual("foo\udca5bar".encode("iso-8859-3", "surrogateescape"),
                          b"foo\xa5bar")
 
+    def test_latin1(self):
+        # Issue6373
+        self.assertEqual("\udce4\udceb\udcef\udcf6\udcfc".encode("latin1", "surrogateescape"),
+                         b"\xe4\xeb\xef\xf6\xfc")
+
 
 def test_main():
     support.run_unittest(