Fix MsgPlayerList being capped to 255

WHY WAS THIS A BYTE.

This prevented having more than 255 people on a server, beyond that the game might get stuck as people's player states wouldn't necessarily get sent.

RELEASE-NOTES.md

@@ -47,7 +47,7 @@ END TEMPLATE-->
 
 ### Other
 
-*None yet*
+* Fix internal networking logic
 
 ### Internal
 

Robust.Server/Player/PlayerManager.cs

@@ -143,7 +143,6 @@ namespace Robust.Server.Player
                 list.Add(info);
             }
             netMsg.Plyrs = list;
-            netMsg.PlyCount = (byte)list.Count;
 
             channel.SendMessage(netMsg);
         }

Robust.Shared/Network/Messages/MsgPlayerList.cs

@@ -12,14 +12,13 @@ namespace Robust.Shared.Network.Messages
     {
         public override MsgGroups MsgGroup => MsgGroups.Core;
 
-        public byte PlyCount { get; set; }
         public List<SessionState> Plyrs { get; set; }
 
         public override void ReadFromBuffer(NetIncomingMessage buffer, IRobustSerializer serializer)
         {
-            Plyrs = new List<SessionState>();
-            PlyCount = buffer.ReadByte();
-            for (var i = 0; i < PlyCount; i++)
+            var playerCount = buffer.ReadInt32();
+            Plyrs = new List<SessionState>(playerCount);
+            for (var i = 0; i < playerCount; i++)
             {
                 var plyNfo = new SessionState
                 {
@@ -34,7 +33,7 @@ namespace Robust.Shared.Network.Messages
 
         public override void WriteToBuffer(NetOutgoingMessage buffer, IRobustSerializer serializer)
         {
-            buffer.Write(PlyCount);
+            buffer.Write(Plyrs.Count);
 
             foreach (var ply in Plyrs)
             {