Importing xpub during wallet creation bugs balances

[matheusd]

It's not recommended to do any other wallet ops while it's still syncing, but this is a reproducible way of bugging out that we might wanna check in the future:

• (tested in spv mode with spvconnect to a local dcrd node)
• Create a wallet with a seed known to have txs
• Start the wallet and enter password for account discovery
• Stop dcrd while the headers are syncing
• Import an xpub
• Restart dcrd
• Let the process finish up
• getbalance returns 0 for the regular accounts

[jrick]

Importing the xpub probably is preventing the wallet from upgrading the cointype to the one for which transactions exist.