Fix broken decode result in multi-thread decoding. (#3782)

Author: tyan0

codec/decoder/core/src/decoder_core.cpp

@@ -2706,7 +2706,6 @@ int32_t DecodeCurrentAccessUnit (PWelsDecoderContext pCtx, uint8_t** ppDst, SBuf
 
         if (iCurrIdD == kuiDependencyIdMax && iCurrIdQ == BASE_QUALITY_ID && isNewFrame) {
           iRet = InitRefPicList (pCtx, pCtx->uiNalRefIdc, pSh->iPicOrderCntLsb);
-          if (iThreadCount > 1) isNewFrame = false;
           if (iRet) {
             pCtx->bRPLRError = true;
             bAllRefComplete = false; // RPLR error, set ref pictures complete flag false