fix: clamp a rowSpan that extends past the last row instead of crashing

[spokodev]

Problem

A cell whose rowSpan reaches beyond the rows below it crashes rendering with an opaque internal error:

const Table = require('cli-table3');
const table = new Table();
table.push([{ content: 'aaaa bbbb', rowSpan: 2 }]); // only one row exists
table.toString();
// TypeError: Cannot read properties of undefined (reading 'length')
//   at insertCell (src/layout-manager.js:121)
//   at addRowSpanCells (src/layout-manager.js:98)

This happens for any rowSpan: N cell with fewer than N rows beneath it, regardless of options.

Cause

addRowSpanCells indexes the target row without checking it exists:

for (let i = 1; i < cell.rowSpan; i++) {
  ...
  insertCell(rowSpanCell, table[rowIndex + i]); // undefined when the span runs past the last row
}

insertCell then reads .length off undefined. The symmetric addColSpanCells mutates the current row in place, so it never indexes a missing row, which is why colSpan past the table width already degrades gracefully while rowSpan crashes.

Fix

Break out of the loop when the target row does not exist, clamping the rowSpan to the table height. This mirrors how colSpan past the width behaves and matches the existing maxHeight = table.length invariant, so out-of-bounds spans render a normal table instead of throwing. In-bounds rendering is byte-for-byte unchanged.

Tests

Added test/issues/rowspan-overflow-test.js asserting that an over-running rowSpan renders instead of throwing. It fails on master (the TypeError) and passes with the fix. Full suite is unchanged (the one pre-existing test custom chars failure is an unrelated no-TTY @colors/colors artifact that also fails on master).