Throw when attempting to add or remove a member's EveryoneRole (#781)

* Throw when attempting to add or remove a member's EveryoneRole

This resolves #780

* Removed braces

src/Discord.Net.Core/Utils/Preconditions.cs

@@ -192,5 +192,13 @@ namespace Discord
                     throw new ArgumentOutOfRangeException(name, "Messages must be younger than two weeks old.");
             }
         }
+        public static void NotEveryoneRole(ulong[] roles, ulong guildId, string name)
+        {
+            for (var i = 0; i < roles.Length; i++)
+            {
+                if (roles[i] == guildId)
+                    throw new ArgumentException($"The everyone role cannot be assigned to a user", name);
+            }
+        }
     }
 }

src/Discord.Net.Rest/DiscordRestApiClient.cs

@@ -392,6 +392,7 @@ namespace Discord.API
             Preconditions.NotEqual(guildId, 0, nameof(guildId));
             Preconditions.NotEqual(userId, 0, nameof(userId));
             Preconditions.NotEqual(roleId, 0, nameof(roleId));
+            Preconditions.NotEqual(roleId, guildId, nameof(roleId), "The Everyone role cannot be added to a user.");
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
@@ -402,6 +403,7 @@ namespace Discord.API
             Preconditions.NotEqual(guildId, 0, nameof(guildId));
             Preconditions.NotEqual(userId, 0, nameof(userId));
             Preconditions.NotEqual(roleId, 0, nameof(roleId));
+            Preconditions.NotEqual(roleId, guildId, nameof(roleId), "The Everyone role cannot be removed from a user.");
             options = RequestOptions.CreateOrClone(options);
 
             var ids = new BucketIds(guildId: guildId);
@@ -1000,6 +1002,8 @@ namespace Discord.API
 
             bool isCurrentUser = userId == CurrentUserId;
 
+            if (args.RoleIds.IsSpecified)
+                Preconditions.NotEveryoneRole(args.RoleIds.Value, guildId, nameof(args.RoleIds));
             if (isCurrentUser && args.Nickname.IsSpecified)
             {
                 var nickArgs = new Rest.ModifyCurrentUserNickParams(args.Nickname.Value ?? "");