Fix Invalid Point error when opening files without position

[asiloisad]

Summary

Fixes TypeError: Invalid Point: (null, null) and Invalid Point: (null, Infinity) errors that occur when opening files without explicit initialLine/initialColumn options.

This commonly happens when opening files outside the current project (e.g., via recent files, drag-and-drop, or external tools).

The Problem

The validation in workspace.open() used !Number.isNaN() to check if position options were provided:

if (!Number.isNaN(options.initialLine)) {
  initialLine = options.initialLine;
}

This is broken because:

• Number.isNaN(null) → false
• !Number.isNaN(null) → true (enters the block)
• initialLine = null (assigns null)
• null >= 0 → true (JavaScript coercion)
• setCursorBufferPosition([null, null]) → Error

The Fix

Replace with Number.isFinite() which correctly rejects null, undefined, NaN, and Infinity:

const hasInitialLine = Number.isFinite(options.initialLine) && options.initialLine >= 0;
const hasInitialColumn = Number.isFinite(options.initialColumn) && options.initialColumn >= 0;
const initialLine = hasInitialLine ? options.initialLine : 0;
const initialColumn = hasInitialColumn ? options.initialColumn : 0;

if (hasInitialLine || hasInitialColumn) {
  // position cursor only when explicitly requested
}

This also fixes a secondary issue where the condition initialLine >= 0 || initialColumn >= 0 was always true (since defaults were 0), causing unnecessary cursor positioning on every file open.

[asiloisad]

The test was failing because Number.isFinite() rejects Infinity, but setCursorBufferPosition can clamp it to the last valid position. Switched to typeof === 'number' && !Number.isNaN() so null/undefined/NaN are still rejected while Infinity passes through for clamping.

[savetheclocktower]

Looks good, but same caveat here as with #1536: a new spec would make this easier to land in time for 1.132.0.

(Sorry for not giving you that feedback when you opened this PR three months ago!)

[asiloisad]

Specs are added 👍.