[FIX] web: add fallback of display_name in formatMany2one.

Since https://github.com/odoo/odoo/pull/137098, we add a fallback for
false display_name in the form view, but we didn't add it for the list
view which doesn't instantiate the Many2one component. It uses
`formatMany2one` instead. Fix it to be consistent with the Many2one

closes odoo/odoo#139215

Signed-off-by: Aaron Bohy (aab) <aab@odoo.com>
Signed-off-by: Rémy Voet (ryv) <ryv@odoo.com>

addons/web/static/src/views/fields/formatters.js

@@ -211,8 +211,10 @@ export function formatInteger(value, options = {}) {
 export function formatMany2one(value, options) {
     if (!value) {
         value = "";
+    } else if (value[1]) {
+        value = value[1];
     } else {
-        value = value[1] || "";
+        value = _t("Unnamed");
     }
     if (options && options.escape) {
         value = encodeURIComponent(value);

addons/web/static/tests/views/fields/formatters_tests.js

@@ -107,6 +107,7 @@ QUnit.module("Fields", (hooks) => {
     QUnit.test("formatMany2one", function (assert) {
         assert.strictEqual(formatMany2one(false), "");
         assert.strictEqual(formatMany2one([false, "M2O value"]), "M2O value");
+        assert.strictEqual(formatMany2one([1, false]), "Unnamed");
         assert.strictEqual(formatMany2one([1, "M2O value"]), "M2O value");
         assert.strictEqual(formatMany2one([1, "M2O value"], { escape: true }), "M2O%20value");
     });

addons/web/static/tests/views/list_view_tests.js

@@ -2560,6 +2560,28 @@ QUnit.module("Views", (hooks) => {
         );
     });
 
+    QUnit.test("many2one field rendering when display_name is falsy", async function (assert) {
+        serverData.models.bar.records[0].display_name = false
+        await makeView({
+            type: "list",
+            resModel: "foo",
+            serverData,
+            arch: '<tree><field name="m2o"/></tree>',
+            mockRPC(route) {
+                assert.step(route);
+            },
+        });
+
+        assert.ok(
+            $(target).find("td:contains(Unnamed)").length,
+            "should have a Unnamed as fallback of many2one display_name"
+        );
+        assert.verifySteps([
+            "/web/dataset/call_kw/foo/get_views",
+            "/web/dataset/call_kw/foo/web_search_read",
+        ]);
+    });
+
     QUnit.test("grouped list view, with 1 open group", async function (assert) {
         await makeView({
             type: "list",