fix LumaLevelToDeltaQP code in combination with getMaxDeltaQP() != 0
in the current VTM code of xGetMinMaxQP(), the LumaLevelToDeltaQP code overwrites any previously determined minQP and maxQP values, especially those set using m_pcEncCfg->getMaxDeltaQP() != 0. This fix makes the LumaLevelToDeltaQP code compatible with m_pcEncCfg->getMaxDeltaQP() != 0, i.e., allows LumaLevelToDeltaQP coding to be used with CU-wise +-X delta-QP search.
Christian Helmrich and Philippe de Lagrange