fix: the ETH line reads unknown at an address no refresh has read (closes #736)

An address's ETH balance is now null until a refresh has read it. That covers
a new address, a new wallet, addresses a wallet scan finds, and every address
after a network switch.

Its line reads `quantity unknown`, Home's balance `unknown (ETH)`, and Send
`Current balance: unknown (ETH)`. Max says the balance is unknown. Send is no
longer refused as zero. The address has no total, and DeleteAddress warns that
it may hold a balance.

A refresh also deletes `balanceNotFetched` only when it read every address in
the stored record.

Model: opus-5-5

src/shared/chainSwitch.js

@@ -49,7 +49,7 @@ function clearPopupCaches() {
 // follow runs first, and this switch is made after it.
 //
 // The save writes only the fields that differ from what this page last saved.
-// When this page last saved a balance of "0", clearing that balance is no
+// When this page last saved a balance of null, clearing that balance is no
 // change. So the switch also resets these fields in the stored record:
 //
 // - every address's balance and token balances;
@@ -100,7 +100,7 @@ async function onChainSwitch(newNetworkId) {
         stored.fraudContracts = [];
         for (const wallet of stored.wallets) {
             for (const addr of wallet.addresses) {
-                addr.balance = "0";
+                addr.balance = null;
                 addr.tokenBalances = [];
             }
         }

src/shared/chainSwitchFields.js

@@ -68,10 +68,11 @@ function applyChainSwitchFields(s, newNetworkId) {
 
     // Clear per-address balances and token balances so stale data
     // from the previous chain is never displayed while the first
-    // refresh on the new chain is in flight.
+    // refresh on the new chain is in flight. A balance of null is one no
+    // refresh has read: it reads as unknown until one has, not as 0.0000.
     for (const wallet of s.wallets || []) {
         for (const addr of wallet.addresses || []) {
-            addr.balance = "0";
+            addr.balance = null;
             addr.tokenBalances = [];
         }
     }
@@ -108,7 +109,7 @@ function copyChainSwitchFields(s, switched) {
     for (const wallet of s.wallets) {
         for (const addr of wallet.addresses) {
             const got = stored.get(addr.address);
-            addr.balance = got ? got.balance : "0";
+            addr.balance = got ? got.balance : null;
             addr.tokenBalances = got ? got.tokenBalances : [];
         }
     }

src/shared/prices.js

@@ -146,7 +146,8 @@ function formatUsd(amount) {
 // way an absent holders_count is not a count of zero.
 //
 //   usd:     the value of the holdings a price is known for, or null when
-//            nothing is knowable at all — testnet, or before the first fetch.
+//            no total can be stated — testnet, before the first fetch, or an
+//            ETH balance no refresh has read.
 //   partial: the address also holds a token with no price, so usd is a floor
 //            and not the total.
 //
@@ -155,7 +156,8 @@ function getAddressValue(addr) {
     const { currentNetwork } = require("./state");
     if (currentNetwork().isTestnet) return { usd: null, partial: false };
     if (!prices.ETH) return { usd: null, partial: false };
-    let usd = parseFloat(addr.balance || "0") * prices.ETH;
+    if (addr.balance == null) return { usd: null, partial: false };
+    let usd = parseFloat(addr.balance) * prices.ETH;
     let partial = false;
     for (const token of addr.tokenBalances || []) {
         // A holding below 0.000001 is left out, as the balance lists leave it