Use more precise error handling in `refreshWalletSummary`

[nuttycom]

At present, receiving an error from getWalletSummary and receiving the None result are conflated; a recurrent error could make the wallet appear to be "stuck at zero" and while the existing logging in getWalletSummary will record the error, it likely needs to propagate upward to somewhere that it can be handled more gracefully and potentially be reported to the user.

Originally posted by @nuttycom in https://github.com/Electric-Coin-Company/zcash-android-wallet-sdk/pull/1372#discussion_r1470399754