Fix definition of an empty IdStringList

Signed-off-by: gatecat <gatecat@ds0.me>

common/idstringlist.h

@@ -35,7 +35,7 @@ struct IdStringList
 {
     SSOArray<IdString, 4> ids;
 
-    IdStringList(){};
+    IdStringList() : ids(1, IdString()){};
     explicit IdStringList(size_t n) : ids(n, IdString()){};
     explicit IdStringList(IdString id) : ids(1, id){};
     template <typename Tlist> explicit IdStringList(const Tlist &list) : ids(list){};