fix(mason_api): login sets in-memory credentials

packages/mason_api/lib/src/mason_api.dart

@@ -175,6 +175,8 @@ class MasonApi {
       throw MasonApiLoginFailure(message: '$error');
     }
 
+    _credentials = credentials;
+
     try {
       return _currentUser = credentials.toUser();
     } catch (error) {
@@ -187,14 +189,15 @@ class MasonApi {
 
   /// Publish universal [bundle] to remote registry.
   Future<void> publish({required List<int> bundle}) async {
-    if (_credentials == null) {
+    var credentials = _credentials;
+
+    if (credentials == null) {
       throw const MasonApiPublishFailure(
         message:
             '''User not found. Please make sure you are logged in and try again.''',
       );
     }
 
-    var credentials = _credentials!;
     if (credentials.areExpired) {
       try {
         credentials = await _refresh();

packages/mason_api/test/src/mason_api_test.dart

@@ -330,6 +330,20 @@ void main() {
           credentials.expiresAt.difference(DateTime.now()).inSeconds,
           closeTo(42, 1),
         );
+
+        try {
+          await masonApi.publish(bundle: <int>[]);
+          fail('should throw');
+        } on MasonApiPublishFailure catch (error) {
+          expect(
+            error.message,
+            isNot(
+              equals(
+                '''User not found. Please make sure you are logged in and try again.''',
+              ),
+            ),
+          );
+        }
       });
     });