fix(storage, windows): getData() crash has been fixed

[russellwheatley]

Description

Two fixes:

1. Use the max size passed in from user instead of artifically created max_size: https://github.com/firebase/flutterfire/compare/storage-12134?expand=1#diff-cd14e729c2a123769d24deb04c095c7e5c520143b9fa4508a63797ebe890fd85R406
2. Check that no error exists, and send result back to the user: https://github.com/firebase/flutterfire/compare/storage-12134?expand=1#diff-cd14e729c2a123769d24deb04c095c7e5c520143b9fa4508a63797ebe890fd85R414

Related Issues

fixes #12134

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