add apply() to pref change

Signed-off-by: Andy Scherzinger <info@andy-scherzinger.de>

src/main/java/com/nextcloud/client/preferences/PreferenceManager.java

@@ -256,7 +256,7 @@ public final class PreferenceManager implements AppPreferences {
 
     @Override
     public void setLegacyClean(boolean isLegacyClean) {
-        preferences.edit().putBoolean(PREF__LEGACY_CLEAN, isLegacyClean);
+        preferences.edit().putBoolean(PREF__LEGACY_CLEAN, isLegacyClean).apply();
     }
 
     @Override