Update PaletteHelper.cs

Author: TheR00st3r

MaterialDesignThemes.Wpf/PaletteHelper.cs

@@ -27,7 +27,7 @@ public virtual void SetLightDark(bool isDark)
 
             var existingMahAppsResourceDictionary = Application.Current.Resources.MergedDictionaries
                 .Where(rd => rd.Source != null)
-                .SingleOrDefault(rd => Regex.Match(rd.Source.OriginalString, @"(\/MahApps.Metro;component\/Styles\/Accents\/)((BaseLight)|(BaseDark))").Success);
+                .SingleOrDefault(rd => Regex.Match(rd.Source.AbsolutePath, @"(\/MahApps.Metro;component\/Styles\/Accents\/)((BaseLight)|(BaseDark))").Success);
             if (existingMahAppsResourceDictionary == null) return;
 
             source =