Fix exception with trying to place entities at... NaN?

This is still a bug but it should not cause an exception on the server

Robust.Server/Placement/PlacementManager.cs

@@ -11,6 +11,7 @@ using System.Linq;
 using Robust.Shared.Enums;
 using Robust.Shared.GameObjects;
 using Robust.Shared.Interfaces.Network;
+using Robust.Shared.Log;
 using Robust.Shared.Maths;
 using Robust.Shared.Network.Messages;
 
@@ -88,6 +89,12 @@ namespace Robust.Server.Placement
 
             var coordinates = msg.EntityCoordinates;
 
+            if (!coordinates.IsValid(_entityManager))
+            {
+                Logger.WarningS("placement",
+                    $"{session} tried to place {msg.ObjType} at invalid coordinate {coordinates}");
+                return;
+            }
 
             /* TODO: Redesign permission system, or document what this is supposed to be doing
             var permission = GetPermission(session.attachedEntity.Uid, alignRcv);