MDEV-33591 MONITOR_INC_VALUE_CUMULATIVE is executed regardless of "if" condition

MONITOR_INC_VALUE_CUMULATIVE is a multiline macro, so the second statement
will be executed always, regardless of "if" condition.

These problems first started with
commit b1ab211d (MDEV-15053).

Thanks to Yury Chaikou from ServiceNow for the report.

storage/innobase/buf/buf0flu.cc

@@ -1389,10 +1389,12 @@ static void buf_flush_LRU_list_batch(ulint max, bool evict,
   mysql_mutex_assert_owner(&buf_pool.mutex);
 
   if (scanned)
+  {
     MONITOR_INC_VALUE_CUMULATIVE(MONITOR_LRU_BATCH_SCANNED,
                                  MONITOR_LRU_BATCH_SCANNED_NUM_CALL,
                                  MONITOR_LRU_BATCH_SCANNED_PER_CALL,
                                  scanned);
+  }
 }
 
 /** Flush and move pages from LRU or unzip_LRU list to the free list.
@@ -1543,15 +1545,19 @@ static ulint buf_do_flush_list_batch(ulint max_n, lsn_t lsn)
     space->release();
 
   if (scanned)
+  {
     MONITOR_INC_VALUE_CUMULATIVE(MONITOR_FLUSH_BATCH_SCANNED,
                                  MONITOR_FLUSH_BATCH_SCANNED_NUM_CALL,
                                  MONITOR_FLUSH_BATCH_SCANNED_PER_CALL,
                                  scanned);
+  }
   if (count)
+  {
     MONITOR_INC_VALUE_CUMULATIVE(MONITOR_FLUSH_BATCH_TOTAL_PAGE,
                                  MONITOR_FLUSH_BATCH_COUNT,
                                  MONITOR_FLUSH_BATCH_PAGES,
                                  count);
+  }
   mysql_mutex_assert_owner(&buf_pool.mutex);
   return count;
 }