workaround for unitialized memory read on import set

+ if we import a set in draw3 (from .xsd file), defcfg won't set _configId in imported params, leaving it uninitialized and leading to strange errors
+ initialize _configId to invalid value, so at worst it will fail in a more comprehensible way
+ we cannot throw from GetConfigId because of the "Caught unhandled unknown exception; terminating" wx behaviour which hides the place in code from which an exception is thrown. Overriding OnUnhandledException and OnExceptionInMainLoop in szapp (and e.g. calling abort, terminate from there) has no effect.
+ introduced a workaround in a completely different part of code than importing set, as the bug in importing set would be hard to find