[Bug] Storage GetBytesAsync crash for gzip-encoded file

### [REQUIRED] Please fill in the following fields:

* Unity editor version: 2019.4.14f1
* Firebase Unity SDK version: 6.15.2 (also tried 7.1.0)
* Source you installed the SDK: Unity Package Manager
* Problematic Firebase Component: Storage
* Other Firebase Components in use: Auth, Database, RemoteConfig, Messaging
* Additional SDKs you are using: none
* Platform you are using the Unity editor on: Mac
* Platform you are targeting: Android
* Scripting Runtime:IL2CPP

### [REQUIRED] Please describe the issue here:

Android client crashes when calling `GetBytesAsync` for a Storage reference that points to a gzip-encoded file. In editor, the method works fine and provides the compressed stream bytes.

#### Steps to reproduce:

What happened? How can we make the problem occur?

- Upload and gzip-encode a file to Firebase storage with e.g. `gsutil cp -Z `
- Call `FirebaseStorage.DefaultInstance.GetReference().GetBytesAsync(1000000)`

On Android device, the call will always crash, even when the file is much, much smaller than the provided limit:

```
2021/03/09 10:16:11.359 6904 7586 Error StorageException StorageException has occurred.
2021/03/09 10:16:11.359 6904 7586 Error StorageException An unknown error occurred, please check the HTTP result code and inner exception for server response.
2021/03/09 10:16:11.359 6904 7586 Error StorageException Code: -13000 HttpResult: 200
2021/03/09 10:16:11.359 6904 7586 Error StorageException The maximum allowed buffer size was exceeded.
2021/03/09 10:16:11.359 6904 7586 Error StorageException java.lang.IndexOutOfBoundsException: The maximum allowed buffer size was exceeded.
2021/03/09 10:16:11.359 6904 7586 Error StorageException at com.google.firebase.storage.internal.cpp.CppByteDownloader.doInBackground(CppByteDownloader.java:55)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at com.google.firebase.storage.StreamDownloadTask.run(com.google.firebase:firebase-storage@@19.1.1:179)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at com.google.firebase.storage.StorageTask.lambda$getRunnable$7(com.google.firebase:firebase-storage@@19.1.1:1072)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at com.google.firebase.storage.StorageTask$$Lambda$12.run(Unknown Source:2)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1162)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:636)
2021/03/09 10:16:11.359 6904 7586 Error StorageException at java.lang.Thread.run(Thread.java:784)
```

My suspicion is that the Android client allocates the byte buffer based on file size in storage. However, the fetch fails to send `accepts: gzip` to the server, which should cause automatic decompression in Google Cloud Storage and the resulting uncompressed stream is too big to fit the buffer, whose size may be based on the compressed size.