synchronizePendingEvents: Fix stuck replaying flag

Similar to change I4628a574, the replaying flag has a chance to become
stuck as true if an exception is thrown while accumulating prunable
replication tasks, which happens before the earlier fix is relevant.
Catch and log the exception and continue since synchronizing with a
subset of prunable tasks isn't much of a problem.

Change-Id: I935c3252e8c3da63ac248b051380558b749ea76e
Release-Notes: Fixed chance for exceptions to block future distributor runs

src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java

diff --git a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
index aa00634..4b5d7c1 100644
--- a/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
+++ b/src/main/java/com/googlesource/gerrit/plugins/replication/ReplicationQueue.java
@@ -225,8 +225,13 @@
       final Map<ReplicateRefUpdate, String> taskNamesByReplicateRefUpdate =
           new ConcurrentHashMap<>();
       if (Prune.TRUE.equals(prune)) {
-        for (Destination destination : destinations.get().getAll(FilterType.ALL)) {
-          taskNamesByReplicateRefUpdate.putAll(destination.getTaskNamesByReplicateRefUpdate());
+        try {
+          for (Destination destination : destinations.get().getAll(FilterType.ALL)) {
+            taskNamesByReplicateRefUpdate.putAll(destination.getTaskNamesByReplicateRefUpdate());
+          }
+        } catch (Throwable e) {
+          repLog.atWarning().withCause(e).log(
+              "Unexpected error while accumulating prunable replication tasks");
         }
       }
       new ChainedScheduler.StreamScheduler<>(