Fix: Block icon on the block switcher may become unreadable.

[jorgefilipecosta]

Description

We were forcing a color change on the icon in cases where there were no available items on the block switcher, but we were not forcing a background color change -- this may make the icon totally invisible. If we force a color chnage we should also force a background color change.

Related: #16349

How has this been tested?

I disabled the group block on the block manager so the group transform is not available.
I pasted the following code on the browser console:

( function() {
	var registerBlockType = wp.blocks.registerBlockType;
	var el = wp.element.createElement;

	registerBlockType( 'test/block', {
		title: 'Test Block',
		icon: { background: '#555d66', foreground: "#fff", src: 'warning' },
		category: 'common',

		edit: function( props ) {
			return el( 'div', { style: { outline: '1px solid gray', padding: 5 } },
                el( 'span', {}, 'My test block' ),
			);
		},

		save: function( props ) {
			return el( 'div', { style: { outline: '1px solid gray', padding: 5 } },
                el( 'span', {}, 'My test block' ),x
			);
		},
	} );
} )();

I inserted the 'Test Block' block, and I verified its icon is visible.

Screenshots

Before:

After:

[talldan]

LGTM 👍