Discover NDK version; handle failure gracefully
Discover NDK version; handle failure gracefully

Handles the case where the user has a different version of the NDK -- for example, `r12` instead of `r12b` -- than the author. Checks for NDK before creating `NDK` directory, to allow reconfiguring and re-running.
tempbottle/rust-ios-android,tempbottle/rust-ios-android,tempbottle/rust-ios-android,tempbottle/rust-ios-android,kennytm/rust-ios-android