fix(miner): port None-metadata guard into paginated status loop

Upstream develop commit feba7e8 (2026-04-18) added `m = m or {}` to the
single-shot `for m in metas:` loop after this branch already rewrote
status() to paginate. Without porting the guard forward, merging this PR
would silently drop jp's fix and crash again on palaces with null-metadata
drawers.

Addresses bensig's review on #851.

mempalace/miner.py

@@ -833,6 +833,7 @@ def status(palace_path: str):
         if not batch:
             break
         for m in batch:
+            m = m or {}
             wing_rooms[m.get("wing", "?")][m.get("room", "?")] += 1
         offset += len(batch)