Add error token in a normal way to the syntax tree as ErrorLeaf.

test/test_parser/test_fast_parser.py

@@ -440,6 +440,7 @@ def test_string_literals():
     """)
 
     script = jedi.Script(dedent(source))
+    script._parser.module().end_pos == (6, 0)
     assert script.completions()