[SPARK-36564][CORE] Fix NullPointerException in LiveRDDDistribution.toApi

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

This PR fixes `NullPointerException` in `LiveRDDDistribution.toApi`.

### Why are the changes needed?

Looking at the stack trace, the NPE is caused by the null `exec.hostPort`. I can't get the complete log to take a close look but only guess that it might be due to the event `SparkListenerBlockManagerAdded` is dropped or out of order.

```
21/08/23 12:26:29 ERROR AsyncEventQueue: Listener AppStatusListener threw an exception
java.lang.NullPointerException
	at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:192)
	at com.google.common.collect.MapMakerInternalMap.putIfAbsent(MapMakerInternalMap.java:3507)
	at com.google.common.collect.Interners$WeakInterner.intern(Interners.java:85)
	at org.apache.spark.status.LiveEntityHelpers$.weakIntern(LiveEntity.scala:696)
	at org.apache.spark.status.LiveRDDDistribution.toApi(LiveEntity.scala:563)
	at org.apache.spark.status.LiveRDD.$anonfun$doUpdate$4(LiveEntity.scala:629)
	at scala.collection.TraversableLike.$anonfun$map$1(TraversableLike.scala:238)
	at scala.collection.mutable.HashMap$$anon$2.$anonfun$foreach$3(HashMap.scala:158)
	at scala.collection.mutable.HashTable.foreachEntry(HashTable.scala:237)
	at scala.collection.mutable.HashTable.foreachEntry$(HashTable.scala:230)
	at scala.collection.mutable.HashMap.foreachEntry(HashMap.scala:44)
	at scala.collection.mutable.HashMap$$anon$2.foreach(HashMap.scala:158)
	at scala.collection.TraversableLike.map(TraversableLike.scala:238)
	at scala.collection.TraversableLike.map$(TraversableLike.scala:231)
	at scala.collection.AbstractTraversable.map(Traversable.scala:108)
	at org.apache.spark.status.LiveRDD.doUpdate(LiveEntity.scala:629)
	at org.apache.spark.status.LiveEntity.write(LiveEntity.scala:51)
	at org.apache.spark.status.AppStatusListener.update(AppStatusListener.scala:1206)
	at org.apache.spark.status.AppStatusListener.maybeUpdate(AppStatusListener.scala:1212)
	at org.apache.spark.status.AppStatusListener.$anonfun$onExecutorMetricsUpdate$6(AppStatusListener.scala:956)
	...
```

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

Yes, users will see the expected RDD info in UI instead of the NPE error.

 ### How was this patch tested?

Pass existing tests.

Closes #33812 from Ngone51/fix-hostport-npe.

Authored-by: yi.wu <yi.wu@databricks.com>
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>
(cherry picked from commit d6c453aaea)
Signed-off-by: Dongjoon Hyun <dongjoon@apache.org>

core/src/main/scala/org/apache/spark/status/LiveEntity.scala

@@ -553,7 +553,7 @@ private class LiveRDDDistribution(exec: LiveExecutor) {
   def toApi(): v1.RDDDataDistribution = {
     if (lastUpdate == null) {
       lastUpdate = new v1.RDDDataDistribution(
-        weakIntern(exec.hostPort),
+        weakIntern(if (exec.hostPort != null) exec.hostPort else exec.host),
         memoryUsed,
         exec.maxMemory - exec.memoryUsed,
         diskUsed,