A function to detect whether init had been called previously, please

[martinellison]

It would be nice to have a way of finding out whether the log had been initialised already (i.e. whether init had been called already). This is because Android apps are often restarted automatically (e.g. when the phone is rotated 90 degrees), which causes a call to Activity.onCreate() in the activity, which may result in a call to android_log::init() in Rust, which is an error after the first time.