added better handling for unexpected error count values

Without more information, the cause of this issue isn't clear. I added code to handle values that are missing or null which should prevent these crashes. I also added debug logging which might help get more details about the cause of this error.

Closes https://gitlab.com/fdroid/acra-crash-reports/-/issues/808 https://gitlab.com/fdroid/acra-crash-reports/-/issues/811