[9.16] Add missing node lock when setting node->wild in rbtdb.c

Backport of MR !7392 (merged)

The write node lock needs to be held when setting node->wild in add_wildcard_magic except when being called from loading_addrdataset which is used to load the zone without locking during its initial load.

(cherry picked from commit 81c24b8d)

Closes #3799 (closed)