Infinite scrollback

[twifty]

In #518 it was mentioned that a large number should be given. In most APIs, if we want to specify such an infinite number, we would either pass -1 or 0.

xterm causes an error for:

1. scrollback: -1, produces: "Invalid array length"
2. scrollback: 0, produces: "cannot read index 0 of undefined"
3. scrollback: Number.MAX_SAFE_INTEGER, produces "Invalid array length"

It appears that JS arrays are limited to an unsigned 32 bit value.

A better approach would be to detect scrollback <= 0 || scrollback > 4294967295 and assign it the max upper value of 4294967295

[Tyriar]

👍 PRs welcome