python interface: replace assert with explicit abort in print_callback
python interface: replace assert with explicit abort in print_callback

This ensures that the error condition is also checked in NASSERT builds
and additionally removes a warning we have seen in NASSERT builds:

	interface/python.cc:342:12: warning: unused variable 'arg_type'
	[-Wunused-variable]
                QualType arg_type = fn->getArgType(i);

Signed-off-by: Tobias Grosser <059b8b880f8441509ec8a65b50b4c6ae74ebea76@grosser.es>
Signed-off-by: Sven Verdoolaege <e5350bbed4977f5eb8ae1dc6abd9ae59d21ace75@kotnet.org>

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