RedisLockRegistry: Don't expire not acquired lock

Fix race condition, when methods `RedisLockRegistry#expireUnusedOlderThan` and `RedisLockRegistry#obtain` are executed successively. 

It's possible to delete the lock from `RedisLockRegistry#expireUnusedOlderThan` method, when lock is created but is not acquired (`RedisLock#getLockedAt = 0`)
It can lead to the situation, when `RedisLockRegistry#obtain` returns multiple locks with the same redis-key, which shouldn't happen at all.

* Skip locks from expiration when their `lockedAt == 0` - new, not acquired yet.

**Cherry-pick to `6.0.x` & `5.5.x`**

spring-integration-redis/src/main/java/org/springframework/integration/redis/util/RedisLockRegistry.java

@@ -81,6 +81,7 @@ import org.springframework.util.ReflectionUtils;
  * @author Artem Bilan
  * @author Vedran Pavic
  * @author Unseok Kim
+ * @author Anton Gabov
  *
  * @since 4.0
  *
@@ -235,7 +236,11 @@ public final class RedisLockRegistry implements ExpirableLockRegistry, Disposabl
 			this.locks.entrySet()
 					.removeIf(entry -> {
 						RedisLock lock = entry.getValue();
-						return now - lock.getLockedAt() > age && !lock.isAcquiredInThisProcess();
+						long lockedAt = lock.getLockedAt();
+						return now - lockedAt > age
+								// 'lockedAt = 0' means that the lock is still not acquired!
+								&& lockedAt > 0
+								&& !lock.isAcquiredInThisProcess();
 					});
 		}
 	}