.clearing._ems: Don't require `first_quote['last']`

Instead just check for the field (which i'm not huge on the key-name for
anyway) and if not found get the "last price" from the real-time shm
buffer's latest 'close' sample.

Unrelatedly, use a `subs.copy()` in the `Router.client_broadcast()` loop
such that if a `client_stream` is popped on connection failure, we don't
RTE for the "size changed on iteration".

piker/clearing/_ems.py

@@ -653,7 +653,11 @@ class Router(Struct):
             flume = feed.flumes[fqme]
             first_quote: dict = flume.first_quote
             book: DarkBook = self.get_dark_book(broker)
-            book.lasts[fqme]: float = float(first_quote['last'])
+
+            if not (last := first_quote.get('last')):
+                last: float = flume.rt_shm.array[-1]['close']
+
+            book.lasts[fqme]: float = float(last)
 
             async with self.maybe_open_brokerd_dialog(
                 brokermod=brokermod,
@@ -716,7 +720,7 @@ class Router(Struct):
             subs = self.subscribers[sub_key]
 
         sent_some: bool = False
-        for client_stream in subs:
+        for client_stream in subs.copy():
             try:
                 await client_stream.send(msg)
                 sent_some = True
@@ -1010,10 +1014,14 @@ async def translate_and_relay_brokerd_events(
                 status_msg.brokerd_msg = msg
                 status_msg.src = msg.broker_details['name']
 
-                await router.client_broadcast(
-                    status_msg.req.symbol,
-                    status_msg,
-                )
+                if not status_msg.req:
+                    # likely some order change state?
+                    await tractor.pause()
+                else:
+                    await router.client_broadcast(
+                        status_msg.req.symbol,
+                        status_msg,
+                    )
 
                 if status == 'closed':
                     log.info(f'Execution for {oid} is complete!')