Ignore ohlc step stream subs lookup errors

piker/data/_sampling.py

@@ -151,7 +151,12 @@ async def iter_ohlc_periods(
         # stream and block until cancelled
         await trio.sleep_forever()
     finally:
+        try:
             subs.remove(ctx)
+        except ValueError:
+            log.error(
+                f'iOHLC step stream was already dropped for {ctx.chan.uid}?'
+            )
 
 
 async def sample_and_broadcast(