Add sleep to fix lag in chat stream

[w4ffl35]

Description

This is a fix for a bug which I identified while attempting to use Chat Stream from within a thread. Adding a sleep within the loop unblocks the thread allowing the chat to stream as expected.
Without this fix, each iteration severely hangs.

Type of Change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

This has been tested within my application which uses llamaindex. My application runs in a separate worker thread which runs properly with all other streaming agents outside of llama index. When I use chat_stream with llama index, it hangs. This code fixes the issue.

Suggested Checklist:

• I have performed a self-review of my own code
• My changes generate no new warnings

[logan-markewich]

@w4ffl35 I'm not 100% this fixes anything? Both with and without this fix the behaviour seems the same. See the test code here
#10290 (comment)

Maybe I'm using flask+streaming wrong though

[w4ffl35]

@logan-markewich did you test with threads?

If the loop enters the continue line after the exception it will lag severely in a loop. I experienced it and lost hours debugging. Adding the sleep fixes it - you can see similar solutions employed in the huggingface workers in transformers for the same reasons as outlined in their commits (which I have since switched to).