[SPARK-33900][WEBUI] Show shuffle read size / records correctly when only remotebytesread is available

### What changes were proposed in this pull request?
Shuffle Read Size / Records can also be displayed in remoteBytesRead>0 localBytesRead=0.

current:
![image](https://user-images.githubusercontent.com/3898450/103079421-c4ca2280-460e-11eb-9e2f-49d35b5d324d.png)
fix:
![image](https://user-images.githubusercontent.com/3898450/103079439-cc89c700-460e-11eb-9a41-6b2882980d11.png)

### Why are the changes needed?
At present, the page only displays the data of Shuffle Read Size / Records when localBytesRead>0.
When there is only remote reading, metrics cannot be seen on the stage page.

### Does this PR introduce _any_ user-facing change?
No

### How was this patch tested?
manual test

Closes #30916 from cxzl25/SPARK-33900.

Authored-by: sychen <[email protected]>
Signed-off-by: Kousuke Saruta <[email protected]>
(cherry picked from commit 700f5ab)
Signed-off-by: Kousuke Saruta <[email protected]>

Author: cxzl25

core/src/main/resources/org/apache/spark/ui/static/stagepage.js

@@ -946,7 +946,8 @@ $(document).ready(function () {
                         },
                         {
                             data : function (row, type) {
-                                if (row.taskMetrics && row.taskMetrics.shuffleReadMetrics && row.taskMetrics.shuffleReadMetrics.localBytesRead > 0) {
+                                if (row.taskMetrics && row.taskMetrics.shuffleReadMetrics &&
+                                    (row.taskMetrics.shuffleReadMetrics.localBytesRead > 0 || row.taskMetrics.shuffleReadMetrics.remoteBytesRead > 0)) {
                                     var totalBytesRead = parseInt(row.taskMetrics.shuffleReadMetrics.localBytesRead) + parseInt(row.taskMetrics.shuffleReadMetrics.remoteBytesRead);
                                     if (type === 'display') {
                                         return formatBytes(totalBytesRead, type) + " / " + row.taskMetrics.shuffleReadMetrics.recordsRead;