[dagster-pipes] start PipesLogReader right away (#25026)

## Summary & Motivation

Looks like there is no reason to have `PipesLogReader` startup be
dependent on `PipesMessageReader` startup.

## How I Tested These Changes

## Changelog

NOCHANGELOG

python_modules/dagster/dagster/_core/pipes/utils.py

@@ -439,20 +439,6 @@ def _logs_thread(
         is_session_closed: Event,
         messages_thread: Thread,
     ) -> None:
-        # Start once we have received the opened message from the external process
-        while True:
-            if self.opened_payload is not None:
-                break
-            # We never received the `opened` message and never will, so don't try to start the log
-            # reader threads.
-            elif not messages_thread.is_alive():
-                return
-            time.sleep(DEFAULT_SLEEP_INTERVAL)
-
-        # Logs are started with a merge of the params generated by the message reader and the opened
-        # payload.
-        log_params = {**params, **self.opened_payload}
-
         wait_for_logs_start = None
 
         # Loop over all log readers and start them if the target is readable, which typically means
@@ -463,16 +449,19 @@ def _logs_thread(
             unstarted_log_readers = {**self.log_readers}
 
             while True:
+                if self.opened_payload is not None:
+                    params = {**params, **self.opened_payload}
+
                 # periodically check for new readers which may be added after the
                 # external process has started and add them to the unstarted log readers
                 for key in self.log_readers:
                     if key not in unstarted_log_readers:
                         unstarted_log_readers[key] = self.log_readers[key]
 
                 for key in list(unstarted_log_readers.keys()).copy():
-                    if unstarted_log_readers[key].target_is_readable(log_params):
+                    if unstarted_log_readers[key].target_is_readable(params):
                         reader = unstarted_log_readers.pop(key)
-                        reader.start(log_params, is_session_closed)
+                        reader.start(params, is_session_closed)
 
                 # In some cases logs might not be written out until after the external process has
                 # exited. That will leave us in this state, where some log readers have not been