[SPARK-31128][WEBUI] Fix Uncaught TypeError in streaming statistics page

### What changes were proposed in this pull request?

There is a minor issue in #26201
In the streaming statistics page, there is such error
```
streaming-page.js:211 Uncaught TypeError: Cannot read property 'top' of undefined
at SVGCircleElement.<anonymous> (streaming-page.js:211)
at SVGCircleElement.__onclick (d3.min.js:1)
```
in the console after clicking the timeline graph.
![image](https://user-images.githubusercontent.com/1097932/76479745-14b26280-63ca-11ea-9079-0065321795f9.png)

This PR is to fix it.
### Why are the changes needed?

Fix the error of javascript execution.

### Does this PR introduce any user-facing change?

No, the error shows up in the console.

### How was this patch tested?

Manual test.

Closes #27883 from gengliangwang/fixSelector.

Authored-by: Gengliang Wang <gengliang.wang@databricks.com>
Signed-off-by: Gengliang Wang <gengliang.wang@databricks.com>

core/src/main/resources/org/apache/spark/ui/static/streaming-page.js

@@ -190,29 +190,32 @@ function drawTimeline(id, data, minX, maxX, minY, maxY, unitY, batchInterval) {
                     .attr("r", function(d) { return isFailedBatch(d.x) ? "2" : "3";});
             })
             .on("click", function(d) {
-                if (lastTimeout != null) {
-                    window.clearTimeout(lastTimeout);
-                }
-                if (lastClickedBatch != null) {
-                    clearBatchRow(lastClickedBatch);
-                    lastClickedBatch = null;
-                }
-                lastClickedBatch = d.x;
-                highlightBatchRow(lastClickedBatch);
-                lastTimeout = window.setTimeout(function () {
-                    lastTimeout = null;
+                var batchSelector = $("#batch-" + d.x);
+                // If there is a corresponding batch row, scroll down to it and highlight it.
+                if (batchSelector.length > 0) {
+                    if (lastTimeout != null) {
+                        window.clearTimeout(lastTimeout);
+                    }
                     if (lastClickedBatch != null) {
                         clearBatchRow(lastClickedBatch);
                         lastClickedBatch = null;
                     }
-                }, 3000); // Clean up after 3 seconds
-
-                var batchSelector = $("#batch-" + d.x);
-                var topOffset = batchSelector.offset().top - 15;
-                if (topOffset < 0) {
-                    topOffset = 0;
+                    lastClickedBatch = d.x;
+                    highlightBatchRow(lastClickedBatch);
+                    lastTimeout = window.setTimeout(function () {
+                        lastTimeout = null;
+                        if (lastClickedBatch != null) {
+                            clearBatchRow(lastClickedBatch);
+                            lastClickedBatch = null;
+                        }
+                    }, 3000); // Clean up after 3 seconds
+
+                    var topOffset = batchSelector.offset().top - 15;
+                    if (topOffset < 0) {
+                        topOffset = 0;
+                    }
+                    $('html,body').animate({scrollTop: topOffset}, 200);
                 }
-                $('html,body').animate({scrollTop: topOffset}, 200);
             });
 }