tsdb/cache: new cacheReader field for tsdb & cache reader

source/dnode/vnode/src/inc/tsdb.h

@@ -851,7 +851,7 @@ typedef struct STsdbReaderInfo {
 typedef struct SCacheRowsReader {
   STsdb          *pTsdb;
   STsdbReaderInfo info;
-  // SVersionRange  verRange;
+  int8_t          cacheReader;  // always true for cache reader
   TdThreadMutex   readerMutex;
   SVnode         *pVnode;
   STSchema       *pSchema;

source/dnode/vnode/src/tsdb/tsdbCacheRead.c

@@ -191,6 +191,7 @@ int32_t tsdbCacherowsReaderOpen(void* pVnode, int32_t type, void* pTableIdList,
   taosThreadMutexInit(&p->readerMutex, NULL);
 
   p->lastTs = INT64_MIN;
+  p->cacheReader = 1;
 
   *pReader = p;
   return TSDB_CODE_SUCCESS;

source/dnode/vnode/src/tsdb/tsdbReadUtil.h

@@ -186,6 +186,7 @@ typedef struct SReaderStatus {
 struct STsdbReader {
   STsdb*             pTsdb;
   STsdbReaderInfo    info;
+  int8_t             cacheReader;  // always false for tsdb reader
   TdThreadMutex      readerMutex;
   EReaderStatus      flag;
   int32_t            code;