fix: a refresh asked for while another runs is no longer dropped (closes #581)

doRefreshAndRender() returned at once when a refresh was already running. An
import asks for a refresh after its address scan, so the addresses the scan
found showed 0.0000 until the next ten-second refresh.

While a refresh runs, a request through ctx now sets a flag. One more refresh
runs once the running one ends. Several requests in that time lead to one more
refresh, not several. A tick of the ten-second timer that finds a refresh
running is still dropped.

Model: opus-5-5

tests/refreshDuringRefresh.test.js

@@ -46,9 +46,9 @@ async function readChain(wallets) {
     }
 }
 
-// Boots the popup over a profile with one wallet. From then on,
-// `refreshBalances()` never returns unless the test answers it. So an unwanted
-// refresh is counted once and then waits, instead of starting more.
+// Boots the popup over a profile with one wallet. From then on, a refresh the
+// test does not answer never returns. So a refresh that starts another on its
+// own is counted and stops, rather than running forever.
 async function boot() {
     const page = await bootPopup(unversionedValidProfile());
     expect(page.pageErrors).toEqual([]);
@@ -111,7 +111,7 @@ async function importKey(page, key) {
     await page.click("btn-add-wallet-confirm");
 }
 
-test("addresses that an import finds during a refresh show their balances once one more refresh returns", async () => {
+test("addresses an import finds while a refresh runs show their balances once one more refresh returns", async () => {
     const { page } = await boot();
     const refresh = await holdRefresh(page);
 
@@ -127,7 +127,7 @@ test("addresses that an import finds during a refresh show their balances once o
     expect(list).toContain("<span>3.0000</span>");
 });
 
-test("several requests during a refresh lead to exactly one more refresh", async () => {
+test("several refreshes asked for while one runs lead to exactly one more", async () => {
     const { page, refreshBalances } = await boot();
     const refresh = await holdRefresh(page);
     const calls = refreshBalances.mock.calls.length;
@@ -143,7 +143,7 @@ test("several requests during a refresh lead to exactly one more refresh", async
     expect(refreshBalances).toHaveBeenCalledTimes(calls + 1);
 });
 
-test("a tick of the ten-second timer during a refresh starts no other refresh", async () => {
+test("a tick of the ten-second timer while a refresh runs queues no other refresh", async () => {
     const { page, refreshBalances } = await boot();
     const refresh = await holdRefresh(page);
     const calls = refreshBalances.mock.calls.length;