Fix issue with gr-select when value is 0

There was an issue with gr-select that when the bound value is 0, the
native value was not set properly because of the way the value was
checked. This change fixes the issue by explicitly checking for
undefined rather than falsy value.

Change-Id: I1ef33cdb99933e5d2a8ba1fd9360266e8d258eaf

polygerrit-ui/app/elements/shared/gr-select/gr-select.js

@@ -34,7 +34,8 @@
     },
 
     _updateValue() {
-      if (this.bindValue) {
+      // It's possible to have a value of 0.
+      if (this.bindValue !== undefined) {
         // Set for chrome/safari so it happens instantly
         this.nativeSelect.value = this.bindValue;
         // Async needed for firefox to populate value. It was trying to do it

polygerrit-ui/app/elements/shared/gr-select/gr-select_test.html

@@ -45,6 +45,11 @@ limitations under the License.
       element = fixture('basic');
     });
 
+    test('value of 0 should still trigger value updates', () => {
+      element.bindValue = 0;
+      assert.equal(element.nativeSelect.value, 0);
+    });
+
     test('bidirectional binding property-to-attribute', () => {
       const changeStub = sinon.stub();
       element.addEventListener('bind-value-changed', changeStub);