credui: Correctly check for duplicated username entries in CredDialogFillUsernameCombo.

dlls/credui/credui_main.c

@@ -160,20 +160,27 @@ static void CredDialogFillUsernameCombo(HWND hwndUsername, const struct cred_dia
         DWORD j;
         BOOL duplicate = FALSE;
 
+        if (!credentials[i]->UserName)
+            continue;
+
         if (params->dwFlags & CREDUI_FLAGS_GENERIC_CREDENTIALS)
         {
-            if ((credentials[i]->Type != CRED_TYPE_GENERIC) || !credentials[i]->UserName)
+            if (credentials[i]->Type != CRED_TYPE_GENERIC)
+            {
+                credentials[i]->UserName = NULL;
                 continue;
             }
-        else
+        }
+        else if (credentials[i]->Type == CRED_TYPE_GENERIC)
         {
-            if (credentials[i]->Type == CRED_TYPE_GENERIC)
+            credentials[i]->UserName = NULL;
             continue;
         }
 
         /* don't add another item with the same name if we've already added it */
         for (j = 0; j < i; j++)
-            if (!strcmpW(credentials[i]->UserName, credentials[j]->UserName))
+            if (credentials[j]->UserName
+                && !strcmpW(credentials[i]->UserName, credentials[j]->UserName))
             {
                 duplicate = TRUE;
                 break;