fix: prompt token may be None in streaming mode#3462

wsa-2002 wants to merge 2 commits intogoogle:maingoogle/adk-python:mainfrom

wsa-2002:prompt-token-count-may-be-none-in-streaming-modewsa-2002/adk-python:prompt-token-count-may-be-none-in-streaming-modeCopy head branch name to clipboard