sqliteBtreeNext
rc = sqliteBtreeNext(pCur, &res);
sqliteBtreeNext(pC->pCursor, &res);
rc = sqliteBtreeNext(pCrsr, &res);
rc = pOp->opcode==OP_Next ? sqliteBtreeNext(pCrsr, &res) :
sqliteBtreeNext(pCrsr, &res);
sqliteBtreeNext(p->pCursor, &res);