fix: use 'is not None and != ""' instead of truthiness for mem0.json merge

The original filter (if v) silently drops False and 0, so
'rerank: false' in mem0.json would be ignored. Use explicit
None/empty-string check to preserve intentional falsy values.

plugins/memory/mem0/__init__.py

@@ -58,7 +58,8 @@ def _load_config() -> dict:
     if config_path.exists():
         try:
             file_cfg = json.loads(config_path.read_text(encoding="utf-8"))
-            config.update({k: v for k, v in file_cfg.items() if v})
+            config.update({k: v for k, v in file_cfg.items()
+                           if v is not None and v != ""})
         except Exception:
             pass