Fix effectively ignored XML parameters for SZ operator

[gregorweiss]

Fixes the problem of ignored parameters from XML file for the SZ operator.

Problem:
The keys in m_Parameter are forced to lower case formatting during Operator construction. Hence, previous checks for corresponding parameters in CompressSZ.cpp always failed, such that parameters set via an XML configuration were effectively ignored.

Solution:
Without changing the enforced lower case formatting in Operator construction, avoiding possible side-effects, and not knowing the reasons for lower case formatting, the current PR suggests the most direct fix in OperatorSZ.cpp.