#20 Refactor - Declare "lottie" as nullable

[young924]

issue #20

[ol-of]

Since content and outValues are nullable, the current implementation of
Java_org_thorvg_lottie_LottieDrawable_nCreateLottie in lottie-libs.cpp can crash because it does not perform any null checks.

Please add null-safety checks to Java_org_thorvg_lottie_LottieDrawable_nCreateLottie, for example:

extern "C" jlong
Java_org_thorvg_lottie_LottieDrawable_nCreateLottie(JNIEnv *env, jclass clazz,
        jstring content, jint length, jintArray out_values) {
    if (content == nullptr || inputStr == nullptr) {
        return 0;
    }
   ...
}

[ol-of]

I’ve left comments regarding the parts that could potentially cause a crash.
For now, please either revert the changes to nCreateLottie or add proper null-checks (NPE handling) in Java_org_thorvg_lottie_LottieDrawable_nCreateLottie.

[young924]

I’ve left comments regarding the parts that could potentially cause a crash. For now, please either revert the changes to nCreateLottie or add proper null-checks (NPE handling) in Java_org_thorvg_lottie_LottieDrawable_nCreateLottie.

I added null-safety checks to Java_org_thorvg_lottie_LottieDrawable_nCreateLottie
Thank you for your comment! @ol-of