Fix ^C not working to end for newer fish + kitty keyboard protocol

[anthonykim1]

Should resolve: microsoft/vscode#295372
We shouldn't read beyond params.length - 1:

xterm.js/src/common/parser/Params.ts

Line 19 in a12061c

* - never read beyond `params.length - 1` (likely to contain arbitrary data)

Reset only sets this.length = 0, it does not zero out underlying array.

So when fish sends CSI = 0 u (one param), params.length is 1, but params.params[1] reads whatever int was left in slot 1 from previous CSI sequence.
SO if that leftover vlaue happens to be 2 or 3, mode becomes 2,3 instead of spec-mandated default 1:

If the modifier field is not present in the escape code, its default value is 1 which means no modifiers. in https://sw.kovidgoyal.net/kitty/keyboard-protocol/#modifiers

[meganrogge]

Nice!