[SPARK-19622][WEBUI] Fix a http error in a paged table when using a `Go` button to search.

## What changes were proposed in this pull request?

The search function of paged table is not available because of we don't skip the hash data of the reqeust path.

![](https://issues.apache.org/jira/secure/attachment/12852996/screenshot-1.png

)

## How was this patch tested?

Tested manually with my browser.

Author: Stan Zhai <zhaishidan@haizhi.com>

Closes #16953 from stanzhai/fix-webui-paged-table.

(cherry picked from commit 021062af)
Signed-off-by: Sean Owen <sowen@cloudera.com>

core/src/main/scala/org/apache/spark/ui/PagedTable.scala

@@ -175,13 +175,14 @@ private[ui] trait PagedTable[T] {
 
       val hiddenFormFields = {
         if (goButtonFormPath.contains('?')) {
-          val querystring = goButtonFormPath.split("\\?", 2)(1)
+          val queryString = goButtonFormPath.split("\\?", 2)(1)
+          val search = queryString.split("#")(0)
           Splitter
             .on('&')
             .trimResults()
             .omitEmptyStrings()
             .withKeyValueSeparator("=")
-            .split(querystring)
+            .split(search)
             .asScala
             .filterKeys(_ != pageSizeFormField)
             .filterKeys(_ != prevPageSizeFormField)