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/popup/views/home.js

@@ -3,6 +3,7 @@ const {
     showView,
     showFlash,
     balanceLinesForAddress,
+    unknownableAmount,
     markTrackedTokensNotFetched,
     isoDate,
     timeAgo,
@@ -76,10 +77,16 @@ function renderTotalValue() {
         if (subEl) subEl.innerHTML = " ";
         return;
     }
-    const ethBal = parseFloat(addr.balance || "0");
-    const ethStr = ethBal.toFixed(4) + " " + nativeCurrency();
-    const ethUsd = ethPrice ? " (" + formatUsd(ethBal * ethPrice) + ")" : "";
-    el.textContent = ethStr + ethUsd;
+    const ethBal = unknownableAmount(addr.balance);
+    if (ethBal === null) {
+        el.textContent = "unknown (" + nativeCurrency() + ")";
+    } else {
+        const ethStr = ethBal.toFixed(4) + " " + nativeCurrency();
+        const ethUsd = ethPrice
+            ? " (" + formatUsd(ethBal * ethPrice) + ")"
+            : "";
+        el.textContent = ethStr + ethUsd;
+    }
 
     if (subEl) {
         subEl.innerHTML =
@@ -411,7 +418,7 @@ function render(ctx) {
             wallet.addresses.push({
                 address: newAddr,
                 index: wallet.nextIndex,
-                balance: "0.0000",
+                balance: null,
                 tokenBalances: [],
             });
             wallet.nextIndex++;
@@ -498,7 +505,8 @@ function init(ctx) {
             return;
         }
         const addr = currentAddress();
-        if (!addr.balance || parseFloat(addr.balance) === 0) {
+        // A null balance is one no refresh has read, so it is not refused.
+        if (parseFloat(addr.balance) === 0) {
             showFlash("Cannot send \u2014 zero balance.");
             return;
         }