Don't fail on leverage tier loading error

closes #8512

freqtrade/exchange/exchange.py

@@ -2431,6 +2431,7 @@ class Exchange:
     def load_cached_leverage_tiers(self, stake_currency: str) -> Optional[Dict[str, List[Dict]]]:
         filename = self._config['datadir'] / "futures" / f"leverage_tiers_{stake_currency}.json"
         if filename.is_file():
+            try:
                 tiers = file_load_json(filename)
                 updated = tiers.get('updated')
                 if updated:
@@ -2439,6 +2440,8 @@ class Exchange:
                         logger.info("Cached leverage tiers are outdated. Will update.")
                         return None
                 return tiers['data']
+            except Exception:
+                logger.exception("Error loading cached leverage tiers. Refreshing.")
         return None
 
     def fill_leverage_tiers(self) -> None: