don't mutate a user's filename
don't mutate a user's filename

if a user specifies ‘test.png’ as their filename, then don’t fuck with
that! now, we were changing that to `’test.png.png’` if they also
specified `format=‘png’`. sure, now they could set their filename
`test.png` and their format `jpeg`, but that is their fault.
this fixes the test, too.

plotly/python-api,ee-in/python-api,plotly/python-api,plotly/plotly.py,plotly/python-api,plotly/plotly.py,ee-in/python-api,ee-in/python-api,plotly/plotly.py