NOOOOO! I'm sorry to hear that and hopefully I can get that fixed up later on. Do you know what pet you had/were fighting, and was it your first/second time going through?
I found approximately 3 bugs all relating to that specific action that was occurring, thank you for noticing it! Those should be fixed in the v0.5 build that's up now.
Edit: I found another bug where searching while a battle starts can also cause a crash. It seems to be the last issue regarding battle starts, hoping I can get that fixed too!
Edit 2: It's all fixed in v0.5.1!