Fix server NRE in console command completions.

Happens if you just type "tp:to<space>" into the console.

Toolshed can fail to provide completion results, in which case a null propagates and possibly crashes the server.

RELEASE-NOTES.md

@@ -44,6 +44,7 @@ END TEMPLATE-->
 ### Bugfixes
 
 * Fix `IClipboardManager.GetText()` returning null in some cases.
+* Fix possible NRE in server-side console command completion code.
 
 ### Other
 

Robust.Server/Console/ServerConsoleHost.cs

@@ -259,6 +259,9 @@ namespace Robust.Server.Console
             }
 
             done:
+
+            result ??= CompletionResult.Empty;
+
             var msg = new MsgConCompletionResp
             {
                 Result = result,

Robust.Shared/Network/Messages/MsgConCompletionResp.cs

@@ -4,14 +4,12 @@ using Robust.Shared.Serialization;
 
 namespace Robust.Shared.Network.Messages;
 
-#nullable disable
-
 public sealed class MsgConCompletionResp : NetMessage
 {
     public override MsgGroups MsgGroup => MsgGroups.Command;
 
     public int Seq { get; set; }
-    public CompletionResult Result { get; set; }
+    public CompletionResult Result { get; set; } = default!;
 
     public override void ReadFromBuffer(NetIncomingMessage buffer, IRobustSerializer serializer)
     {