close plt only if shown

[AakashKeswani]

• Closing the plt before returning the figure renders it useless. Therefore we should close the plt only if shown.

[grzesir]

Since this library no longer seems to be maintained, we have created a duplicate of it that we plan to maintain and improve over time. If you'd like to use our version check it out here: https://github.com/Lumiwealth/quantstats_lumi

Please feel free to fork and send your pull request to this new library, we will be actively monitoring the library and approving PRs