Fix module reloading incorrectly on exception

[SigmathBits]

Pull request summary

Currently when reloading a module, if there is an exception in Bot.load_module, such as on import, the module is improperly restored and left out of Bot._modules (since it gets removed by Bot.unload_module). This causes an issue where you can't load, unload, or reload the module again without restarting the bot. This PR fixes this issue.

Checklist

• [x] If code changes were made then they have been tested.
  • [ ] I have updated the documentation to reflect the changes.
  • [x] I have updated the changelog with a quick recap of my changes.
• [x] This PR fixes an issue.
• [ ] This PR adds something new (e.g. new method or parameters).
• [ ] This PR is a breaking change (e.g. methods or parameters removed/renamed)
• [ ] This PR is not a code change (e.g. documentation, README, ...)

[IAmTomahawkx]

Please add a changelog entry, other than that looks good

[SigmathBits]

Alright, done! Is that sufficient?

[IAmTomahawkx]

lgtm, thanks