Add check theme support is an array before indexing

[mkaz]

Description

Adds checks for return value from get_theme_support to validate it returns an array of at least size 1 that can be indexed into.

The get_theme_support may return false, and attempting to indexing causes a PHP notice.

Fixes #23085

How has this been tested?

Use a theme that does not support Global Styles, I had a Twenty Nineteen theme, but may not have been the most up-to-date.

Turn on PHP notice warnings as visible.

Load editor. Confirm warning does not show after fix.

Types of changes

Adds a couple of additional checks of the value returned from get_theme_support()

[github-actions]

Size Change: +113 B (0%)

Total Size: 1.13 MB

Filename	Size	Change
build/block-editor/index.js	106 kB	+25 B (0%)
build/block-editor/style-rtl.css	12.1 kB	+66 B (0%)
build/block-editor/style.css	12.1 kB	+67 B (0%)
build/block-library/editor-rtl.css	7.88 kB	+1 B
build/block-library/index.js	129 kB	-60 B (0%)
build/blocks/index.js	48.1 kB	+3 B (0%)
build/components/index.js	195 kB	+4 B (0%)
build/edit-widgets/index.js	9.33 kB	-2 B (0%)
build/editor/index.js	44.8 kB	+9 B (0%)
build/format-library/index.js	7.72 kB	-1 B
build/plugins/index.js	2.56 kB	+1 B

ℹ️ View Unchanged

Filename	Size	Change
build/a11y/index.js	1.14 kB	0 B
build/annotations/index.js	3.62 kB	0 B
build/api-fetch/index.js	3.4 kB	0 B
build/autop/index.js	2.83 kB	0 B
build/blob/index.js	620 B	0 B
build/block-directory/index.js	7.22 kB	0 B
build/block-directory/style-rtl.css	892 B	0 B
build/block-directory/style.css	892 B	0 B
build/block-library/editor.css	7.89 kB	0 B
build/block-library/style-rtl.css	7.96 kB	0 B
build/block-library/style.css	7.96 kB	0 B
build/block-library/theme-rtl.css	684 B	0 B
build/block-library/theme.css	686 B	0 B
build/block-serialization-default-parser/index.js	1.88 kB	0 B
build/block-serialization-spec-parser/index.js	3.1 kB	0 B
build/components/style-rtl.css	19.5 kB	0 B
build/components/style.css	19.5 kB	0 B
build/compose/index.js	9.31 kB	0 B
build/core-data/index.js	11.4 kB	0 B
build/data-controls/index.js	1.29 kB	0 B
build/data/index.js	8.44 kB	0 B
build/date/index.js	5.47 kB	0 B
build/deprecated/index.js	772 B	0 B
build/dom-ready/index.js	568 B	0 B
build/dom/index.js	3.17 kB	0 B
build/edit-navigation/index.js	8.26 kB	0 B
build/edit-navigation/style-rtl.css	975 B	0 B
build/edit-navigation/style.css	974 B	0 B
build/edit-post/index.js	303 kB	0 B
build/edit-post/style-rtl.css	5.6 kB	0 B
build/edit-post/style.css	5.6 kB	0 B
build/edit-site/index.js	16.6 kB	0 B
build/edit-site/style-rtl.css	2.96 kB	0 B
build/edit-site/style.css	2.96 kB	0 B
build/edit-widgets/style-rtl.css	2.4 kB	0 B
build/edit-widgets/style.css	2.4 kB	0 B
build/editor/editor-styles-rtl.css	423 B	0 B
build/editor/editor-styles.css	423 B	0 B
build/editor/style-rtl.css	4.26 kB	0 B
build/editor/style.css	4.27 kB	0 B
build/element/index.js	4.64 kB	0 B
build/escape-html/index.js	733 B	0 B
build/format-library/style-rtl.css	502 B	0 B
build/format-library/style.css	502 B	0 B
build/hooks/index.js	2.13 kB	0 B
build/html-entities/index.js	622 B	0 B
build/i18n/index.js	3.56 kB	0 B
build/is-shallow-equal/index.js	710 B	0 B
build/keyboard-shortcuts/index.js	2.51 kB	0 B
build/keycodes/index.js	1.94 kB	0 B
build/list-reusable-blocks/index.js	3.12 kB	0 B
build/list-reusable-blocks/style-rtl.css	226 B	0 B
build/list-reusable-blocks/style.css	226 B	0 B
build/media-utils/index.js	5.29 kB	0 B
build/notices/index.js	1.79 kB	0 B
build/nux/index.js	3.4 kB	0 B
build/nux/style-rtl.css	616 B	0 B
build/nux/style.css	613 B	0 B
build/primitives/index.js	1.5 kB	0 B
build/priority-queue/index.js	789 B	0 B
build/redux-routine/index.js	2.85 kB	0 B
build/rich-text/index.js	14.8 kB	0 B
build/server-side-render/index.js	2.68 kB	0 B
build/shortcode/index.js	1.7 kB	0 B
build/token-list/index.js	1.28 kB	0 B
build/url/index.js	4.06 kB	0 B
build/viewport/index.js	1.85 kB	0 B
build/warning/index.js	1.14 kB	0 B
build/wordcount/index.js	1.17 kB	0 B

_{compressed-size-action}

[oandregal]

There's the gutenberg_experimental_get function that Jorge created recently. I was thinking that we could perhaps modify it in such a way that it does type checking and if the first parameter is not an array it returns a void array. Then we can do gutenberg_experimental_get( get_theme_support( 'editor-color-palette' ), '0' ) and avoid the nesting levels type checking requires for this code. We're going to do more of checking theme support for other things so this would be very useful.

[mkaz]

I updated the PR with the change suggested, the one thing I don't really like is the check gets added into the function, when technically it shouldn't need it. The function should be able to assume it was called correctly, but it does simplify things.