AttributeError: '_io.TextIOWrapper' object has no attribute 'getvalue'

Was debugging an AWS Lambda, trying to set `sys.stdout`

```
Traceback (most recent call last):
File "/var/task/wdb/ui.py", line 193, in loop
stop = self.interact()
File "/var/task/wdb/ui.py", line 240, in interact
rv = fun(data)
File "/var/task/wdb/ui.py", line 469, in do_eval
self.db.hooked = self.handle_exc()
File "/var/lang/lib/python3.6/contextlib.py", line 89, in __exit__
next(self.gen)
File "/var/task/wdb/__init__.py", line 653, in capture_output
out.extend(sys.stdout.getvalue().splitlines())
File "/var/task/project/hooks.py", line 59, in __getattr__
return getattr(self._replaced, attr)
File "/var/runtime/awslambda/bootstrap.py", line 361, in __getattr__
return getattr(self._fd, attr)
AttributeError: '_io.TextIOWrapper' object has no attribute 'getvalue'

```

Start with capture_output in wdb/__init__.py at the failing getvalue call, then review the AWS Lambda traceback and the stdout delegation shown in project/hooks.py. Reproduce the Lambda-specific behavior if possible; done should mean output capture no longer raises this AttributeError while handling the reported execution path.

Written by the indexing model from the issue text.