SOLR-17637: Fix LBHttpSolrClient & HttpShardHandler bug (#3147)

This bug causes async requests to be uncompleted in some error scenarios.
The HttpShardHandler can hang indefinitely when this happens.

(cherry picked from commit db0cbd3)

Author: HoustonPutman

solr/CHANGES.txt

@@ -5,30 +5,15 @@ Most people will find the solr-upgrade-notes.adoc file more approachable.
 https://github.com/apache/solr/blob/main/solr/solr-ref-guide/modules/upgrade-notes/pages/solr-upgrade-notes.adoc
 
 ==================  9.8.1 ==================
-New Features
----------------------
-(No changes)
-
-Improvements
----------------------
-(No changes)
-
-Optimizations
----------------------
-(No changes)
-
 Bug Fixes
 ---------------------
-(No changes)
+* SOLR-17637: LBHttp2SolrClient can fail to complete async requests in certain error scenarios.
+  This can cause the HttpShardHandler to indefinitely wait on a completed response that will never come. (Houston Putman)
 
 Dependency Upgrades
 ---------------------
 (No changes)
 
-Other Changes
----------------------
-(No changes)
-
 ==================  9.8.0 ==================
 New Features
 ---------------------

solr/solrj/src/java/org/apache/solr/client/solrj/impl/LBHttp2SolrClient.java

@@ -236,7 +236,7 @@ public void onFailure(Exception e, boolean retryReq) {
               String url;
               try {
                 url = it.nextOrError(e);
-              } catch (SolrServerException ex) {
+              } catch (Throwable ex) {
                 apiFuture.completeExceptionally(e);
                 return;
               }

solr/solrj/src/java/org/apache/solr/client/solrj/impl/LBSolrClient.java

@@ -303,7 +303,9 @@ public synchronized String nextOrError(Exception previousEx) throws SolrServerEx
       }
       // Skipping check time exceeded for the first request
       // Ugly string based hack but no live servers message here is VERY misleading :(
-      if ((previousEx != null && previousEx.getMessage().contains("Limits exceeded!"))
+      if ((previousEx != null
+              && previousEx.getMessage() != null
+              && previousEx.getMessage().contains("Limits exceeded!"))
           || (numServersTried > 0 && isTimeExceeded(timeAllowedNano, timeOutTime))) {
         throw new SolrServerException(
             "The processing limits for to this request were exceeded, see cause for details",