[FIX] web_editor: prevent error on undefined closest Node

Summary:
	page with 2 popups (newsletter popup and regular popup), cookie
	bar all justaposed. Chatbot window also open. For some reason
	closestBlock(testedNode) is undefined (testedNode) is a #text
	Node. Change already in place for 16.3

Cause:
	no preventive measure for null value before creating
	a node iterator on the value.Node in dom does not have
	an ancestor of type block.

Solution:
	backport solution from 16.3, return false when currentNodeParentBlock
	is null, since preceding and following would also be undefined,
	return false.

opw-3395673

closes odoo/odoo#132590

X-original-commit: 8a72f669813bc7d8aa9038d75e08ecef00b70e01
Signed-off-by: David Monjoie (dmo) <dmo@odoo.com>
Co-authored-by: Pedro Manuel Calheiros Lima de Sousa <peso@odoo.com>

addons/web_editor/static/src/js/editor/odoo-editor/test/spec/utils.test.js

@@ -404,6 +404,11 @@ describe('Utils', () => {
             const result = closestBlock(p);
             window.chai.expect(result).to.equal(p);
         });
+        it('should return null if no block ancestor', () => {
+            const node = document.createTextNode('\n        ');
+            window.chai.expect(closestBlock(node)).to.equal(null);
+            window.chai.expect(isVisibleTextNode(node)).to.equal(false);
+        });
     });
     describe('lastLeaf', () => {
         it('should find the last leaf of a child-rich block', () => {