Ignore setting m_lock_rows if lock_type == TL_IGNORE (facebook#871) (facebook#871)

Summary:
Original report: https://jira.mariadb.org/browse/MDEV-15816

To reproduce this bug just following below steps,

client 1:
USE test;
CREATE TABLE t1 (i INT) ENGINE=MyISAM;
HANDLER t1 OPEN h;
CREATE TABLE t2 (i INT) ENGINE=RocksDB;
LOCK TABLES t2 WRITE;

client 2:
FLUSH TABLES WITH READ LOCK;

client 1:
INSERT INTO t2 VALUES (1);

So client 1 acquired the lock and set m_lock_rows = RDB_LOCK_WRITE.
Then client 2 calls store_lock(TL_IGNORE) and m_lock_rows was wrongly
set to RDB_LOCK_NONE, as below

```
 #0  myrocks::ha_rocksdb::store_lock (this=0x7fffbc03c7c8, thd=0x7fffc0000ba0, to=0x7fffc0011220, lock_type=TL_IGNORE)
 #1  get_lock_data (thd=0x7fffc0000ba0, table_ptr=0x7fffe84b7d20, count=1, flags=2)
 #2  mysql_lock_abort_for_thread (thd=0x7fffc0000ba0, table=0x7fffbc03bbc0)
 #3  THD::notify_shared_lock (this=0x7fffc0000ba0, ctx_in_use=0x7fffbc000bd8, needs_thr_lock_abort=true)
 #4  MDL_lock::notify_conflicting_locks (this=0x555557a82380, ctx=0x7fffc0000cc8)
 #5  MDL_context::acquire_lock (this=0x7fffc0000cc8, mdl_request=0x7fffe84b8350, lock_wait_timeout=2)
 #6  Global_read_lock::lock_global_read_lock (this=0x7fffc0003fe0, thd=0x7fffc0000ba0)
```

Finally, client 1 "INSERT INTO..." hits the Assertion 'm_lock_rows == RDB_LOCK_WRITE'
failed in myrocks::ha_rocksdb::write_row()

Fix this bug by not setting m_locks_rows if lock_type == TL_IGNORE.

Closes facebook#838
Pull Request resolved: facebook#871

Differential Revision: D9417382

Pulled By: lth

Author: minggr

Diff for: mysql-test/suite/rocksdb/r/lock.result

@@ -106,3 +106,18 @@ SELECT a,b FROM t1;
 a	b
 UNLOCK TABLES;
 DROP TABLE t1, t2;
+CREATE TABLE t1 (i INT) ENGINE=MyISAM;
+HANDLER t1 OPEN h;
+CREATE TABLE t2 (i INT) ENGINE=RocksDB;
+LOCK TABLES t2 WRITE;
+connect  con1,localhost,root,,test;
+connection con1;
+FLUSH TABLES WITH READ LOCK;
+connection default;
+INSERT INTO t2 VALUES (1);
+UNLOCK TABLES;
+HANDLER h CLOSE;
+connection con1;
+disconnect con1;
+connection default;
+DROP TABLE t1, t2;

Diff for: mysql-test/suite/rocksdb/t/lock.test

@@ -196,6 +196,28 @@ SELECT a,b FROM t1;
 UNLOCK TABLES;
 DROP TABLE t1, t2;
 
+CREATE TABLE t1 (i INT) ENGINE=MyISAM;
+HANDLER t1 OPEN h;
+CREATE TABLE t2 (i INT) ENGINE=RocksDB;
+LOCK TABLES t2 WRITE;
+
+--connect (con1,localhost,root,,test)
+--connection con1
+--send
+FLUSH TABLES WITH READ LOCK;
+
+--connection default
+INSERT INTO t2 VALUES (1);
+UNLOCK TABLES;
+HANDLER h CLOSE;
+
+--connection con1
+--reap
+--disconnect con1
+
+--connection default
+DROP TABLE t1, t2;
+
 # Check that all connections opened by test cases in this file are really
 # gone so execution of other tests won't be affected by their presence.
 --source include/wait_until_count_sessions.inc

Diff for: storage/rocksdb/ha_rocksdb.cc

@@ -10402,7 +10402,7 @@ THR_LOCK_DATA **ha_rocksdb::store_lock(THD *const thd, THR_LOCK_DATA **to,
     m_lock_rows = RDB_LOCK_WRITE;
   } else if (lock_type == TL_READ_WITH_SHARED_LOCKS) {
     m_lock_rows = RDB_LOCK_READ;
-  } else {
+  } else if (lock_type != TL_IGNORE) {
     m_lock_rows = RDB_LOCK_NONE;
     if (THDVAR(thd, lock_scanned_rows)) {
       /*