conflux: Avoid non fatal assert in CIRCUIT_IS_CONFLUX()

In the circuit_about_to_free(), we clear the circ->conflux object and then we
end up trying to emit an event on the control port which calls
CIRCUIT_IS_CONFLUX() and non fatal assert on the false branch.

Fixes #41037

Signed-off-by: David Goulet <dgoulet@torproject.org>

changes/ticket41037

+  o Minor bugfix (conflux):
+    - Avoid a non fatal assert when describing a conflux circuit on the control
+      port after being prepped to be freed. Fixes bug 41037; bugfix on 0.4.8.15.

src/core/or/conflux_util.h

@@ -28,8 +28,9 @@ CIRCUIT_IS_CONFLUX(const circuit_t *circ)
       tor_assert_nonfatal(circ->purpose == CIRCUIT_PURPOSE_CONFLUX_LINKED);
     return true;
   } else {
-    tor_assert_nonfatal(circ->purpose != CIRCUIT_PURPOSE_CONFLUX_LINKED);
-    tor_assert_nonfatal(circ->purpose != CIRCUIT_PURPOSE_CONFLUX_UNLINKED);
+    /* We don't assert on purposes here because we can end up in this branch
+     * with circ->conflux being NULL but for a conflux purpose. This happens in
+     * the about_to_free() code path. */
     return false;
   }
 }