HBASE-23056 Block count is 0 when BucketCache using persistent IOEngine and retrieve from file

Signed-off-by: Reid Chan <reidchan@apache.org>

Author: ZhaoBQ

hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/BucketCache.java

@@ -1094,6 +1094,7 @@ private void retrieveFromFile(int[] bucketSizes) throws IOException {
       }
       parsePB(BucketCacheProtos.BucketCacheEntry.parseDelimitedFrom(in));
       bucketAllocator = new BucketAllocator(cacheCapacity, bucketSizes, backingMap, realCacheSize);
+      blockNumber.add(backingMap.size());
     }
   }