fix: don't default to uncharged sprite state for cells (#38730)

Content.Client/PowerCell/PowerCellSystem.cs

@@ -48,8 +48,9 @@ public sealed class PowerCellSystem : SharedPowerCellSystem
         if (!_sprite.LayerExists((uid, args.Sprite), PowerCellVisualLayers.Unshaded))
             return;
 
+        // If no appearance data is set, rely on whatever existing sprite state is set being correct.
         if (!_appearance.TryGetData<byte>(uid, PowerCellVisuals.ChargeLevel, out var level, args.Component))
-            level = 0;
+            return;
 
         var positiveCharge = level > 0;
         _sprite.LayerSetVisible((uid, args.Sprite), PowerCellVisualLayers.Unshaded, positiveCharge);