add: error handling in firestore-internal for version extension

[Seung-o]

Discussion

• Bug: Async Problem

I think firebase-internal.ts has async problem. It goes to if-else state before credential is created. So, in my case, I normally send credential in nestJS project with applicationDefault() method and credential was consoled out to be instance ServiceAccountCredential, but it gave error.

So, I suggest using try-catch statement in firestore-internal.ts and it would handle origin error. Also, in 'else' case It returns original credential.

Testing

• I did all the test
• Success percentage was 99.4 % ( 3 errors occurred )
• 3 errors was engaged with FirestoreSerivce constructor, but i did not modify it.

API Changes

• There is no API Changes.

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