fix "blank mnemonic" errors when using only seed

This is a follow up to #486 which was reverted because of a failed test which should now pass

src/js/index.js

@@ -210,7 +210,7 @@
         network.onSelect();
         adjustNetworkForSegwit();
         if (seed != null) {
-            phraseChanged();
+            seedChanged()
         }
         else {
             rootKeyChanged();
@@ -225,12 +225,7 @@
         else {
             DOM.bip32path.prop("readonly", true);
             clients[clientIndex].onSelect();
-            if (seed != null) {
-                phraseChanged();
-            }
-            else {
-                rootKeyChanged();
-            }
+            rootKeyChanged();
         }
     }
 
@@ -455,7 +450,9 @@
         else {
             network = libs.bitcoin.networks.litecoinXprv;
         }
-        phraseChanged();
+        // Can't use rootKeyChanged because validation will fail as we changed
+        // the network but the version bytes stayed as previously.
+        seedChanged();
     }
 
     function toggleSplitMnemonic() {
@@ -601,7 +598,7 @@
     }
 
     function bitcoinCashAddressTypeChange() {
-        phraseChanged();
+        rootKeyChanged();
     }
 
     function toggleIndexes() {

tests/spec/tests.js

@@ -3045,6 +3045,25 @@ it('Uses the correct derivation for altcoins with root keys', function(done) {
     });
 });
 
+// Changing the coin when only using a seed (without a mnemonic phrase) should
+// work the same as the previous test.
+// See https://github.com/iancoleman/bip39/pull/486
+it('Uses the correct derivation for altcoins with seed and without mnemonic phrase', function(done) {
+    driver.findElement(By.css('.seed'))
+        .sendKeys("20da140d3dd1df8713cefcc4d54ce0e445b4151027a1ab567b832f6da5fcc5afc1c3a3f199ab78b8e0ab4652efd7f414ac2c9a3b81bceb879a70f377aa0a58f3");
+    driver.sleep(generateDelay).then(function() {
+        // 4) switch from bitcoin to viacoin
+        selectNetwork("VIA - Viacoin");
+        driver.sleep(generateDelay).then(function() {
+            // 5) ensure the derived address is correct
+            getFirstAddress(function(address) {
+                expect(address).toBe("Vq9Eq4N5SQnjqZvxtxzo7hZPW5XnyJsmXT");
+                done();
+            });
+        });
+    });
+});
+
 // Selecting a language with no existing phrase should generate a phrase in
 // that language.
 it('Generate a random phrase when language is selected and no current phrase', function(done) {