fix(query): check for null ptr.

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

@@ -2534,6 +2534,7 @@ int32_t initDelSkylineIterator(STableBlockScanInfo* pBlockScanInfo, STsdbReader*
 
   int32_t code = 0;
   SArray* pDelData = taosArrayInit(4, sizeof(SDelData));
+  ASSERT(pReader->pReadSnap != NULL);
 
   SDelFile* pDelFile = pReader->pReadSnap->fs.pDelFile;
   if (pDelFile && taosArrayGetSize(pReader->pDelIdx) > 0) {
@@ -2640,6 +2641,8 @@ static int32_t moveToNextFile(STsdbReader* pReader, SBlockNumber* pBlockNum) {
 
   taosArrayDestroy(pIndexList);
 
+  if (pReader->pReadSnap != NULL) {
+
     SDelFile* pDelFile = pReader->pReadSnap->fs.pDelFile;
     if (pReader->pDelFReader == NULL && pDelFile != NULL) {
       int32_t code = tsdbDelFReaderOpen(&pReader->pDelFReader, pDelFile, pReader->pTsdb);
@@ -2659,6 +2662,7 @@ static int32_t moveToNextFile(STsdbReader* pReader, SBlockNumber* pBlockNum) {
         return code;
       }
     }
+  }
 
   return TSDB_CODE_SUCCESS;
 }