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

tests/deleteAddress.test.js

@@ -33,6 +33,7 @@ const USDC = "0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48";
 const EMPTY = { address: "0x1", balance: "0.0000", tokenBalances: [] };
 const ETH_ONLY = { address: "0x1", balance: "1.5", tokenBalances: [] };
 const DUST = { address: "0x1", balance: "0.00001", tokenBalances: [] };
+const NOT_READ = { address: "0x1", balance: null, tokenBalances: [] };
 const TOKEN_ONLY = {
     address: "0x1",
     balance: "0.0000",
@@ -106,14 +107,23 @@ describe("whether an address holds anything", () => {
         expect(addressHoldsFunds(DUST)).toBe(true);
     });
 
+    // No refresh has read it, so the address may hold funds.
+    test("an ETH balance no refresh has read counts", () => {
+        expect(addressHoldsFunds(NOT_READ)).toBe(true);
+    });
+
     test("an address holding nothing does not", () => {
         expect(addressHoldsFunds(EMPTY)).toBe(false);
         expect(addressHoldsFunds(ZERO_TOKEN)).toBe(false);
     });
 
-    test("a missing address or missing fields do not", () => {
+    test("a missing address does not", () => {
         expect(addressHoldsFunds(undefined)).toBe(false);
-        expect(addressHoldsFunds({ address: "0x1" })).toBe(false);
+    });
+
+    // It reads as unknown, as a null balance does.
+    test("an address with no ETH balance field counts", () => {
+        expect(addressHoldsFunds({ address: "0x1" })).toBe(true);
     });
 });
 
@@ -140,6 +150,20 @@ describe("the balance warning on the removal confirmation", () => {
         expect(html).toContain("<span>0.0000</span>");
     });
 
+    test("an ETH balance no refresh has read is warned about, and reads as unknown", () => {
+        const html = balanceWarningHtml(NOT_READ);
+        expect(html).toContain("This address may hold a balance.");
+        expect(html).not.toContain("This address holds a balance.");
+        expect(html).toContain("quantity unknown");
+        expect(html).not.toContain("0.0000");
+    });
+
+    test("an address with no ETH balance field reads the same", () => {
+        expect(balanceWarningHtml({ address: "0x1" })).toContain(
+            "This address may hold a balance.",
+        );
+    });
+
     // The sentence must not assert an amount, because any amount it could
     // assert has been rounded: "This address holds 0.0000 ETH." is what the
     // rounded form produces for an address that holds real money.