added assertion

git-svn-id: svn://svn.code.sf.net/p/magicseteditor/code/trunk@1548 0fc631ac-6414-0410-93d0-97cfa31319b6

src/data/pack.cpp

@@ -384,6 +384,7 @@ void PackGenerator::reset(int seed) {
 }
 
 PackInstance& PackGenerator::get(const String& name) {
+	assert(set);
 	PackInstanceP& instance = instances[name];
 	if (instance) {
 		return *instance;