prevent recurrence of CID 1397192

Coverity found a possible double free in CID 1397192, which dgoulet dismissed as a False Positive. I think I found the logic by which Coverity considered a double free possible. The done block in test_intro_point_registration() has some calls to tt_assert() that can jump backwards if the assertion fails, causing a double free in that unlikely event.

The block that tests hs_circuitmap_free_all() should probably be in a helper function with its own done label that doesn't lead to a double free if the assertion fails.

For reasons I don't understand, it looks like the renames in 6bacc3c7a88509043613d3bc29534c0ecf8803b1 caused Coverity to no longer see this potential double free, even though it looks like it changed nothing relevant.