Issue #13959: Fix a logic bug.

Lib/imp.py

@@ -45,7 +45,7 @@ def load_module(name, file, filename, details):
 
     """
     suffix, mode, type_ = details
-    if mode and (not mode.startswith(('r', 'U'))) or '+' in mode:
+    if mode and (not mode.startswith(('r', 'U')) or '+' in mode):
         raise ValueError('invalid file open mode {!r}'.format(mode))
     elif file is None and type_ in {PY_SOURCE, PY_COMPILED}:
         msg = 'file object required for import (type code {})'.format(type_)