vault discovery fix

src/blockchain/wallet.js

@@ -100,6 +100,9 @@ let pendingOrders = []
 function discoverVaults() {
   const s = useStore()
   const owner = s.account
+  if( owner === null )
+    s.vaults = []
+  else
     _discoverVaults(owner).then((result)=>{
       if( s.account === owner ) { // double-check the account since it could have changed during our await
         s.vaults = result