BUG: Fix bug where sort_index if unsorted levels.

[tshauck]

Closes #12261

[tshauck]

Not sure if this is the best way to solve this, but it looks like the bug in #12261 is because the labels are sorted, but the levels aren't.

It seems like the better way is is_lexsorted should return False if the levels aren't sorted because you could get the potential mismatch, but that's a layer below this issue so I didn't want to touch it.

[jreback]

this is not the right way to go about this.

[tshauck]

Ok... Does this help you see what this issue is enough (you didn't seem to have an idea from the issue*) to recommend what the appropriate path would be?

• Seems to be the level sorting issue unless it's a red herring.

[jreback]

yeh I haven't really delved into it much.

[tshauck]

Ok...