feat(theme): should have auto behaviour when theme option is empty

Author: Joxit

src/components/docker-registry-ui.riot

@@ -101,7 +101,7 @@ along with this program. If not, see <http://www.gnu.org/licenses/>.
         <li>
           <a href="https://github.com/Joxit/docker-registry-ui/blob/main/LICENSE">License AGPL-3.0</a>
         </li>
-        <li if="{ props.theme === 'auto' }">
+        <li if="{ props.theme === 'auto' || props.theme === '' }">
           <material-switch
             on-change="{ onThemeChange }"
             checked="{ state.themeSwitch }"

src/scripts/theme.js

@@ -34,7 +34,7 @@ const normalizeKey = (k) =>
     .replace(/^theme-/, '');
 
 const preferDarkMode = ({ theme }) => {
-  if (theme === 'auto') {
+  if (theme === 'auto' || theme === "") {
     switch (localStorage.getItem(LOCAL_STORAGE_THEME)) {
       case 'dark':
         return true;