Sorry, only just saw this. This is fixed in the next version which isn't released yet, but in the meantime you can progress past this using the console. Google the steps to enable the console in Ren'py, then once you've done the steps, load your save and progress to part with through that text conversation. Then open the console with Shift+O, and type the below exactly as written (Case sensitive)
messageCount = 1
Then press enter. It should then let you keep playing beyond the end of that text conversation.