SortedLedgerStorage > Spammy log on mem-table size limit reached

**BUG REPORT**

When the Bookie tries to flush the MemEntryTable on an `addEntry` it started to spam the log "Reached size null".

***Describe the bug***
```
20-05-04-00-02-44 Reached size null
java.io.FileNotFoundException: /data/magnews/bookie/./bookie_data/current/73/72/67372.idx (Too many open files)
at java.base/java.io.RandomAccessFile.open0(Native Method)
at java.base/java.io.RandomAccessFile.open(RandomAccessFile.java:345)
at java.base/java.io.RandomAccessFile.(RandomAccessFile.java:259)
at java.base/java.io.RandomAccessFile.(RandomAccessFile.java:214)
at org.apache.bookkeeper.bookie.FileInfo.readHeader(FileInfo.java:213)
at org.apache.bookkeeper.bookie.FileInfo.checkOpen(FileInfo.java:310)
at org.apache.bookkeeper.bookie.FileInfo.checkOpen(FileInfo.java:278)
at org.apache.bookkeeper.bookie.FileInfo.size(FileInfo.java:388)
at org.apache.bookkeeper.bookie.IndexPersistenceMgr.updatePage(IndexPersistenceMgr.java:642)
at org.apache.bookkeeper.bookie.IndexInMemPageMgr.grabLedgerEntryPage(IndexInMemPageMgr.java:447)
at org.apache.bookkeeper.bookie.IndexInMemPageMgr.getLedgerEntryPage(IndexInMemPageMgr.java:412)
at org.apache.bookkeeper.bookie.IndexInMemPageMgr.putEntryOffset(IndexInMemPageMgr.java:571)
at org.apache.bookkeeper.bookie.LedgerCacheImpl.putEntryOffset(LedgerCacheImpl.java:108)
at org.apache.bookkeeper.bookie.InterleavedLedgerStorage.processEntry(InterleavedLedgerStorage.java:539)
at org.apache.bookkeeper.bookie.SortedLedgerStorage.process(SortedLedgerStorage.java:271)
at org.apache.bookkeeper.bookie.EntryMemTable.flushSnapshot(EntryMemTable.java:256)
at org.apache.bookkeeper.bookie.EntryMemTable.flush(EntryMemTable.java:206)
at org.apache.bookkeeper.bookie.SortedLedgerStorage$1.run(SortedLedgerStorage.java:300)
at java.base/java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:515)
at java.base/java.util.concurrent.FutureTask.run(FutureTask.java:264)
at java.base/java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:304)
at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
at java.base/java.lang.Thread.run(Thread.java:834)

```

***Expected behavior***

I expect that if it can't flush the checkpoint for this type of Exception the service stops