Supply current GuildChannel Name if not specified

src/Discord.Net/Entities/Channels/GuildChannel.cs

@@ -55,6 +55,10 @@ namespace Discord
 
             var args = new ModifyGuildChannelParams();
             func(args);
+
+            if (!args.Name.IsSpecified)
+                args.Name = Name;
+
             var model = await Discord.ApiClient.ModifyGuildChannelAsync(Id, args).ConfigureAwait(false);
             Update(model, UpdateSource.Rest);
         }

src/Discord.Net/Entities/Channels/TextChannel.cs

@@ -36,6 +36,10 @@ namespace Discord
 
             var args = new ModifyTextChannelParams();
             func(args);
+
+            if (!args.Name.IsSpecified)
+                args.Name = Name;
+
             var model = await Discord.ApiClient.ModifyGuildChannelAsync(Id, args).ConfigureAwait(false);
             Update(model, UpdateSource.Rest);
         }

src/Discord.Net/Entities/Channels/VoiceChannel.cs

@@ -33,6 +33,10 @@ namespace Discord
 
             var args = new ModifyVoiceChannelParams();
             func(args);
+
+            if (!args.Name.IsSpecified)
+                args.Name = Name;
+
             var model = await Discord.ApiClient.ModifyGuildChannelAsync(Id, args).ConfigureAwait(false);
             Update(model, UpdateSource.Rest);
         }