fix(grid): prevent NaN column width when hidden grid has all columns sized - 21.2.x

[viktorkombov]

Closes #17418

Description

getPossibleColumnWidth() divided the available width by columnsToSize when every visible column already had an explicit or constrained width.

When the grid is hidden through a wrapper and has no measurable width, calcWidth falls back to the sum of the column widths. In this case, computedWidth equals sumExistingWidths and columnsToSize is 0, resulting in 0 / 0 = NaN. This then poisons the cached column widths and can cause an infinite sizing loop.

When the grid is using the column-width sum fallback and there are no columns left to auto-size, return the "0px" sentinel so the existing valid column widths are preserved.

Motivation / Context

Type of Change (check all that apply):

• Bug fix
• New functionality
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Refactoring (no functional changes)
• Documentation
• Demos
• CI/CD
• Tests
• Changelog
• Skills/Agents

Component(s) / Area(s) Affected:

How Has This Been Tested?

• Unit tests
• Manual testing
• Automated e2e tests

Test Configuration:

• Angular version:
• Browser(s):
• OS:

Screenshots / Recordings

Checklist:

• All relevant tags have been applied to this PR
• This PR includes unit tests covering all the new code (test guidelines)
• This PR includes API docs for newly added methods/properties (api docs guidelines)
• This PR includes feature/README.MD updates for the feature docs
• This PR includes general feature table updates in the root README.MD
• This PR includes CHANGELOG.MD updates for newly added functionality
• This PR contains breaking changes
• This PR includes ng update migrations for the breaking changes (migrations guidelines)
• This PR includes behavioral changes and the feature specification has been updated with them
• Accessibility (ARIA, keyboard navigation, focus management) has been verified

[Copilot]

Pull request overview

Fixes a grid column auto-sizing edge case where getPossibleColumnWidth() can produce NaN when the grid is hidden (no measurable width) and all visible columns already have explicit/constrained widths, which can poison cached widths and lead to a sizing loop.

Changes:

• Added a guard in IgxGridBaseDirective.getPossibleColumnWidth() to return the "0px" sentinel in the hidden-width-sum fallback scenario.
• Added a regression unit test that hides the grid via a display:none wrapper and verifies derived widths remain finite.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
projects/igniteui-angular/grids/grid/src/grid-base.directive.ts	Adds an early-return to avoid deriving invalid column widths when grid width is computed via column-width-sum fallback.
projects/igniteui-angular/grids/grid/src/column.spec.ts	Adds a regression test that reproduces the hidden-grid sizing scenario and asserts no NaN widths are derived.