Only update gallery flag if fetch result is explicitly boolean

This adds the flag to the destructuring of the fetch callback (so it is
not binding to the stale closure value), and also conditionally updates
the global only if the type is explicitly boolean. This avoids a
scenario in which updates to other editor settings which omit the
gallery flag property result in the global value being overwritten with
`undefined`.

packages/editor/src/components/provider/index.native.js

@@ -91,12 +91,7 @@ class NativeEditorProvider extends Component {
 	}
 
 	componentDidMount() {
-		const {
-			capabilities,
-			locale,
-			updateSettings,
-			galleryWithImageBlocks,
-		} = this.props;
+		const { capabilities, locale, updateSettings } = this.props;
 
 		updateSettings( {
 			...capabilities,
@@ -149,8 +144,10 @@ class NativeEditorProvider extends Component {
 		);
 
 		this.subscriptionParentUpdateEditorSettings = subscribeUpdateEditorSettings(
-			( editorSettings ) => {
-				window.wp.galleryBlockV2Enabled = galleryWithImageBlocks;
+			( { galleryWithImageBlocks, ...editorSettings } ) => {
+				if ( typeof galleryWithImageBlocks === 'boolean' ) {
+					window.wp.galleryBlockV2Enabled = galleryWithImageBlocks;
+				}
 				updateSettings( this.getThemeColors( editorSettings ) );
 			}
 		);