HBASE--28666 Dropping unclosed WALTailingReaders leads to leaked sock…

…ets (#5994)

In WALEntryStream, always use current WALTailingReader if one exists

Signed-off-by: Duo Zhang <zhangduo@apache.org>
(cherry picked from commit bd8ad45)

hbase-server/src/main/java/org/apache/hadoop/hbase/replication/regionserver/WALEntryStream.java

@@ -220,6 +220,7 @@ private HasNext prepareReader() {
             // we will read from the beginning so we should always clear the compression context
             reader.resetTo(-1, true);
           }
+          return HasNext.YES;
         } catch (FileNotFoundException e) {
           // For now, this could happen only when reading meta wal for meta replicas.
           // In this case, raising UncheckedIOException will let the endpoint deal with resetting