Decal fix (#21761)

- Don't send stale chunks for deleted grid as client just errors it anyway.
- Store some allocations in fields.

Content.Server/Decals/DecalSystem.cs

@@ -454,9 +454,7 @@ namespace Content.Server.Decals
                     previouslySent.Remove(netGrid);
 
                     // Was the grid deleted?
-                    if (!TryGetEntity(netGrid, out var gridId) || !MapManager.IsGrid(gridId.Value))
-                        staleChunks[netGrid] = oldIndices;
-                    else
+                    if (TryGetEntity(netGrid, out var gridId) && !MapManager.IsGrid(gridId.Value))
                     {
                         // If grid was deleted then don't worry about telling the client to delete the chunk.
                         oldIndices.Clear();