[lldb] Make TestIOHandlerResizeNoEditline pass with Python 2

io.BytesIO seems to produce a stream in Python 2 which isn't recognized
as a file object in the SWIG API, so this test fails for Python 2 (and I assume
also an old SWIG version needs to be involved).

Instead just open an empty input file which is a file object in all Python
versions to make this test pass everywhere.