Fix empty topic verify (#3833)

Author: niksaveliev

ydb/core/client/server/msgbus_server_persqueue.cpp

@@ -65,7 +65,7 @@ TProcessingResult ProcessMetaCacheSingleTopicsResponse(
                 MSTATUS_ERROR,
                 NPersQueue::NErrorCode::UNKNOWN_TOPIC,
                 Sprintf("path '%s' has unknown/invalid root prefix '%s', Marker# PQ14",
-                        fullPath.c_str(), entry.Path[0].c_str()),
+                        fullPath.c_str(), entry.Path.empty() ? "" :entry.Path[0].c_str()),
                 true
             };
         }

ydb/core/client/server/msgbus_server_pq_metacache.cpp

@@ -511,9 +511,10 @@ class TPersQueueMetaCacheActor : public TActorBootstrapped<TPersQueueMetaCacheAc
 
         for (const auto& [path, database] : waiter->GetTopics()) {
             auto split = NKikimr::SplitPath(path);
-            Y_ABORT_UNLESS(!split.empty());
             TSchemeCacheNavigate::TEntry entry;
-            entry.Path.insert(entry.Path.end(), split.begin(), split.end());
+            if (!split.empty()) {
+                entry.Path.insert(entry.Path.end(), split.begin(), split.end());
+            }
 
             entry.SyncVersion = waiter->SyncVersion;
             entry.ShowPrivatePath = waiter->ShowPrivate;

ydb/services/persqueue_v1/actors/persqueue_utils.cpp

@@ -37,7 +37,7 @@ TProcessingResult ProcessMetaCacheTopicResponse(const TSchemeCacheNavigate::TEnt
             return TProcessingResult {
                     Ydb::PersQueue::ErrorCode::ErrorCode::BAD_REQUEST,
                     Sprintf("path '%s' has unknown/invalid root prefix '%s', Marker# PQ14",
-                            fullPath.c_str(), entry.Path[0].c_str()),
+                            fullPath.c_str(), entry.Path.empty() ? "" : entry.Path[0].c_str()),
                     true
             };
         }