Exception when switching buffer after resize

Problem

An exception is thrown (latest master and probably before) if we resize the screen to a bigger dimension while being in the alt screen buffer. Once the alt screen buffer exists and we switch back to the normal buffer, the exception will show up, and the terminal will stop working (blank screen).

I think this has the same root cause as #838 and likely others where the line or row data is an undefined reference.

How to reproduce

• Start the demo
• Run a command that uses the alt screen buffer (e.g. vim)
• Change the rows and/or cols value to a higher value (it happens in both cases)
• Exit the app to switch back to the normal buffer

Demo

[mofux]

You’re a genius, thanks @Tyriar!

[Tyriar]

The same also breaks when rows change in the other direction, the scrollbar shows there is more content but you can’t scroll it (because they’re blank lines).