Make sure margin gets updated

[Link1J]

Closes #431

Not sure if there was something else planned, but basically reverting two small changes from #406 fixes the issue.

Well, only the TextBuffer::edit_end one fixes the reported issue, but there was no point leaving the issue in the undo/redo code.

[lhecker]

Oh, so that's why I called reflow(false) there previously. 😄
That said, this PR is incorrect. You need to test these changes on large files, particularly with word-wrap - the performance issue will be very obvious then.

[lhecker]

These two removed lines are old, from the initial import. I've since added dirty tracking in the ICU code which makes resetting self.search superfluous.

[Link1J]

I didn't think of the performance issues of reflowing all the time. Probably what I get for trying to solve a simple issue on a phone.

But wouldn't it possibly need to reflow if the margin size changes? My code wasn't performent, but did at least allow for that to happen.

[lhecker]

But wouldn't it possibly need to reflow if the margin size changes?

end_edit code already recomputes the updated line statistics and cursor positions. But you're right, because after the margin changes, we may have to do it again. Weird thing is that this worked in my testing. It's probably a niche issue and hard to notice. I'll fix it.