fix: impove behavior when loading old backtest results

freqtrade/data/btanalysis/bt_fileutils.py

@@ -312,18 +312,25 @@ def get_backtest_market_change(filename: Path, include_ts: bool = True) -> pd.Da
     return df
 
 
-def get_backtest_wallet_change(filename: Path, strategy_name: str) -> pd.DataFrame:
+def get_backtest_wallet_change(filename: Path, strategy_name: str) -> pd.DataFrame | None:
     """
     Read backtest wallet change file.
     :param filename: Path to the backtest result zip file
     :param strategy_name: Name of the strategy to load
     :return: DataFrame with wallet change data
     """
-    data = load_file_from_zip(filename, f"{filename.stem}_{strategy_name}_wallet.feather")
-    df = pd.read_feather(BytesIO(data))
+    if filename.suffix != ".zip":
+        return None
 
-    df.loc[:, "__date_ts"] = df.loc[:, "date"].astype(np.int64) // 1000 // 1000
-    return df
+    try:
+        data = load_file_from_zip(filename, f"{filename.stem}_{strategy_name}_wallet.feather")
+        df = pd.read_feather(BytesIO(data))
+
+        df.loc[:, "__date_ts"] = df.loc[:, "date"].astype(np.int64) // 1000 // 1000
+        return df
+    except ValueError:
+        pass
+    return None
 
 
 def find_existing_backtest_stats(