Fix ChronicleMap leak through Closeable in ChronicleMapBuilder.establishCleanupThread()

src/main/java/net/openhft/chronicle/map/ChronicleMapBuilder.java

@@ -1814,11 +1814,12 @@ public final class ChronicleMapBuilder<K, V> implements
         // WARNING this relies on the fact that ReplicatedChronicleMap closes closeables in the same
         // order as they are added, i. e. OldDeletedEntriesCleanupThread instance close()d before
         // the following closeable
+        String mapIdentityString = map.toIdentityString();
         map.addCloseable(() -> {
             try {
                 cleanupThread.join();
             } catch (InterruptedException e) {
-                LOG.warn(map.toIdentityString() +
+                LOG.warn(mapIdentityString +
                         ": Interrupted while waiting for the cleanup thread to cease");
                 Thread.currentThread().interrupt();
             }