fix(mdSelect): Close menu on hitting Enter key

call `checkCloseMenu(ev)` with `ev` argument.
ensure references to `ev` are non-null

Fixes #4377. Closes #4384.

Author: shuding

src/components/select/select.js

@@ -1058,7 +1058,7 @@ function SelectProvider($$interimElementProvider) {
                 });
                 ev.preventDefault();
               }
-              checkCloseMenu();
+              checkCloseMenu(ev);
               break;
             case keyCodes.TAB:
             case keyCodes.ESCAPE:
@@ -1122,7 +1122,7 @@ function SelectProvider($$interimElementProvider) {
            */
           function mouseOnScrollbar() {
             var clickOnScrollbar = false;
-            if(ev.currentTarget.children.length > 0) {
+            if(ev && (ev.currentTarget.children.length > 0)) {
               var child = ev.currentTarget.children[0];
               var hasScrollbar = child.scrollHeight > child.clientHeight;
               if (hasScrollbar && child.children.length > 0) {