The parameter could have an offset of 0xffff/0xfffe, in which case the
parameter name should be the name of the function, rather than NULL.

This means that the string is NULL so don't attempt to access the
string data in this case.

Move it before loading of the constant data to allow better debugging
of problems during the processing of loading the constant data.

Also removes dirtifying of SCISSORTESTENABLE state that is made
redundant by ActivateContext(...,CTXUSAGE_CLEAR).

comctl32: Push down function scope variable into the different case statements which allows us using more specific types in case.