Flex layout scrolling bug

[smithbm2316]

This contains a fix for #796. However, I'm opening this PR as I think there might be a bit to discuss about the flex layout, as I'm having a bit of trouble figuring out the real culprit. As far as I can see, I don't know how layout_config could end up being a nil value, every occurrence I see of it in Telescope has it fallback to an empty table at the very least, so I'm not sure how it ever becomes a nil value. I could possibly use a hand in debugging this further.

What I have here feels more like a temporary workaround than actually fixing the real problem though. I'll be continuing to work on figuring out the real underlying issue here the coming day or two.

[Conni2461]

There is a good chance that #823 also addresses this issue because layout_defaults have a default table after these changes. See https://github.com/nvim-telescope/telescope.nvim/pull/823/files#diff-4936325bfc521d7cffc09fe0156becd4a4ba2ed169431c94bd63669fe0cc1a2aR89-R97

So i am not sure if its worth fixing it right now.

[smithbm2316]

There is a good chance that #823 also addresses this issue because layout_defaults have a default table after these changes. See https://github.com/nvim-telescope/telescope.nvim/pull/823/files#diff-4936325bfc521d7cffc09fe0156becd4a4ba2ed169431c94bd63669fe0cc1a2aR89-R97

So i am not sure if its worth fixing it right now.

I had a feeling that this might be this case. I made this mostly as a way for the person who opened #796 would have a temporary workaround so their environment wouldn't break. I'll keep an eye on that PR to see if it ends up fixing this issue as well.

[Conni2461]

No longer needed, i can no longer reproduce this issue with the latest changes. Still thanks @smithbm2316 :)