fix: Handle missing SSL context in multiprocess populate

When use_tls=False, the connection doesn't have an SSL context (ctx),
so check if it exists before trying to delete it.

Fixes #1374

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: dimitri-yatsenko

src/datajoint/autopopulate.py

@@ -525,7 +525,8 @@ def handler(signum, frame):
                 else:
                     # spawn multiple processes
                     self.connection.close()
-                    del self.connection._conn.ctx  # SSLContext is not pickleable
+                    if hasattr(self.connection._conn, "ctx"):
+                        del self.connection._conn.ctx  # SSLContext is not pickleable
                     with (
                         mp.Pool(processes, _initialize_populate, (self, self.jobs, populate_kwargs)) as pool,
                         tqdm(desc="Processes: ", total=nkeys)