Finally solve the last-price-is-`nan` issue..

Not sure why I put this off for so long but the check is in now such
that if the market isn't open or no rt quote comes in from the first
query, we just pull from the last shm history 'close' value.
Includes another fix to avoid raising when a double remove on the client
side stream from the registry sometimes happens.

piker/clearing/_ems.py

@@ -20,6 +20,7 @@ In da suit parlances: "Execution management systems"
 """
 from contextlib import asynccontextmanager
 from dataclasses import dataclass, field
+from math import isnan
 from pprint import pformat
 import time
 from typing import AsyncIterator, Callable
@@ -959,6 +960,12 @@ async def process_client_order_cmds(
                 # like every other shitty tina platform that makes
                 # the user choose the predicate operator.
                 last = dark_book.lasts[fqsn]
+
+                # sometimes the real-time feed hasn't come up
+                # so just pull from the latest history.
+                if isnan(last):
+                    last = feed.shm.array[-1]['close']
+
                 pred = mk_check(trigger_price, last, action)
 
                 spread_slap: float = 5
@@ -1146,8 +1153,14 @@ async def _emsd_main(
                     )
 
                 finally:
-                    # remove client from "registry"
+                    # try to remove client from "registry"
+                    try:
                         _router.clients.remove(ems_client_order_stream)
+                    except KeyError:
+                        log.warning(
+                            f'Stream {ems_client_order_stream._ctx.chan.uid}'
+                            ' was already dropped?'
+                        )
 
                     dialogues = _router.dialogues