UI: Fix crash on patronJsonThread

If a user exit obs while patronJsonThread is running, the thread crashed
with the error below.
  QThread: Destroyed while thread is still running

(cherry picked from commit b21edafe98)
This commit is contained in:
Internal Server Error - Gitea: Git with a cup of tea
500 Internal Server Error

Gitea Version: 1.28.0+dev-477-g8b6ad49a5f