FirebaseFirestore.LogLevel crash if no instance was created #888

[REQUIRED] Please fill in the following fields:

• Unity editor version: 2020.1
• Firebase Unity SDK version: 6.16.1
• Source you installed the SDK: UPM (.unitypackage or Unity Package Manager)
• Problematic Firebase Component: Firestore (Auth, Database, etc.)
• Other Firebase Components in use: Auth, RemoteConfig(Auth, Database, etc.)
• Additional SDKs you are using: Google sign in (Facebook, AdMob, etc.)
• Platform you are using the Unity editor on: Mac (Mac, Windows, or Linux)
• Platform you are targeting: Android (iOS, Android, and/or desktop)
• Scripting Runtime: IL2CPP(Mono, and/or IL2CPP)

[REQUIRED] Please describe the issue here:

get crash:

After FirebaseApp is ready, call:
FirebaseFirestore.setLoggingEnabled(true);

crash

#00 pc 0000000000203360 /data/app/com.iscoolentertainment.snc-uASpMzKBwqBTylOAvW-FkA==/lib/arm64/libFirebaseCppApp-6_16_1.so (_JNIEnv::CallStaticVoidMethod(_jclass*, _jmethodID*, ...)+72) (BuildId: 53fcddeb61b159ccb0507acde42d344e)
E/CRASH: #1 pc 0000000000225c64 /data/app/com.iscoolentertainment.snc-uASpMzKBwqBTylOAvW-FkA==/lib/arm64/libFirebaseCppApp-6_16_1.so (firebase::firestore::Firestore::set_log_level(firebase::LogLevel)+44) (BuildId: 53fcddeb61b159ccb0507acde42d344e)

workaround:

Have to create an Instance first

var db = FirebaseFirestore.DefaultInstance;
FirebaseFirestore.LogLevel = Debug.isDebugBuild ? LogLevel.Debug : LogLevel.Error;

do not crash

In firestore_android.cc, bool FirestoreInternal::Initialize(App* app) must before anything else, I suppose that it's called on the first Instance Creation. Did not test ios.