OpenSIPS version you are running

• all version

Describe the bug
When fix_nated_contact() is called after topology_hiding(), the generated Contact is a concatenation of the two values, which is invalid.

To Reproduce

Run topology hiding and call fix_nated_contact() on an initial INVITE after topology_hiding() is engaged.

Expected behavior

A valid Contact header should result, most likely the one generated by fix_nated_contact().