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

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

Author: Wim van der Ham

src/components/ScriptExplorer/ScriptEntry.jsx

@@ -228,7 +228,7 @@ class ScriptEntry extends React.Component {
     } else {
       this.setState({
         fetchedUTXOs: false,
-        fetchUTXOsError: "Failed to fetch UTXOs.",
+        fetchUTXOsError: "This address has a zero balance.",
       });
     }
   };