Some other X Pack preparations

src/KKdLib/txp.cpp

@@ -427,3 +427,8 @@ bool txp_set::unpack_file_modern(const void* data, size_t size, uint32_t signatu
         ret = unpack_file(st.data.data(), st.header.use_big_endian);
     return ret;
 }
+
+txp_set& txp_set::operator=(const txp_set& set) {
+    textures.assign(set.textures.begin(), set.textures.end());
+    return *this;
+}