`kraken`: Explicitly report missing `Pair` fields in error

piker/brokers/kraken/feed.py

@@ -352,7 +352,13 @@ async def stream_quotes(
             # transform to upper since piker style is always lower
             sym = sym.upper()
             sym_info = await client.symbol_info(sym)
+            try:
                 si = Pair(**sym_info)  # validation
+            except TypeError:
+                fields_diff = set(sym_info) - set(Pair.__struct_fields__)
+                raise TypeError(
+                    f'Missing msg fields {fields_diff}'
+                )
             syminfo = si.to_dict()
             syminfo['price_tick_size'] = 1 / 10**si.pair_decimals
             syminfo['lot_tick_size'] = 1 / 10**si.lot_decimals