only cache expensive case

lib/wallet.py

@@ -1765,15 +1765,15 @@ class Abstract_Wallet(PrintError):
             return result
         if self.txi.get(txid, {}) != {}:
             result = self.average_price(txid, price_func, ccy) * txin_value/Decimal(COIN)
+            self.coin_price_cache[cache_key] = result
+            return result
         else:
             fiat_value = self.get_fiat_value(txid, ccy)
             if fiat_value is not None:
-                result = fiat_value
+                return fiat_value
             else:
                 p = self.price_at_timestamp(txid, price_func)
-                result = p * txin_value/Decimal(COIN)
-        self.coin_price_cache[cache_key] = result
-        return result
+                return p * txin_value/Decimal(COIN)
 
 
 class Simple_Wallet(Abstract_Wallet):