fix(scriptexplorer): Change the error message for spending from new wallet

[wfjvdham]

For a new wallet no UTXO's can be found. This results in an uninformative error message. The message is now changed to having 0 balance.

ISSUES: #172

Description

Does this PR introduce a breaking change?

• [ ] Yes
• [X] No

Does this PR fix an open issue?

• [X] Yes
• [ ] No