Made parameters more consistent, added checks against the ImageFormat

src/Discord.Net.Core/CDN.cs

@@ -56,10 +56,13 @@ namespace Discord
         /// <returns>
         ///     A URL pointing to the guild's icon in the specified size.
         /// </returns>
-        public static string GetGuildIconUrl(ulong guildId, string iconId, ushort size, ImageFormat format)
+        public static string GetGuildIconUrl(ulong guildId, string iconId, ImageFormat format, ushort size)
         {
             if (string.IsNullOrWhiteSpace(iconId))
                 return null;
+            if (format == ImageFormat.Gif)
+                throw new ArgumentException("Requested image format mustn't be a gif.");
+
             string extension = FormatToExtension(format, iconId);
             return $"{DiscordConfig.CDNUrl}icons/{guildId}/{iconId}.{extension}?size={size}";
         }

src/Discord.Net.Rest/Entities/Guilds/RestGuild.cs

@@ -60,7 +60,7 @@ namespace Discord.Rest
         public ulong DefaultChannelId => Id;
         /// <inheritdoc />
         public string GetIconUrl(ImageFormat format = ImageFormat.Auto, ushort size = 128)
-            => CDN.GetGuildIconUrl(Id, IconId, size, format);
+            => CDN.GetGuildIconUrl(Id, IconId, format, size);
         /// <inheritdoc />
         public string SplashUrl => CDN.GetGuildSplashUrl(Id, SplashId);
 

src/Discord.Net.Rest/Entities/Guilds/RestUserGuild.cs

@@ -21,7 +21,7 @@ namespace Discord.Rest
         public DateTimeOffset CreatedAt => SnowflakeUtils.FromSnowflake(Id);
         /// <inheritdoc />
         public string GetIconUrl(ImageFormat format = ImageFormat.Auto, ushort size = 128)
-            => CDN.GetGuildIconUrl(Id, _iconId, size, format);
+            => CDN.GetGuildIconUrl(Id, _iconId, format, size);
 
         internal RestUserGuild(BaseDiscordClient discord, ulong id)
             : base(discord, id)

src/Discord.Net.WebSocket/Entities/Guilds/SocketGuild.cs

@@ -98,7 +98,7 @@ namespace Discord.WebSocket
         public DateTimeOffset CreatedAt => SnowflakeUtils.FromSnowflake(Id);
         /// <inheritdoc />
         public string GetIconUrl(ImageFormat format = ImageFormat.Auto, ushort size = 128)
-            => CDN.GetGuildIconUrl(Id, IconId, size, format);
+            => CDN.GetGuildIconUrl(Id, IconId, format, size);
         /// <inheritdoc />
         public string SplashUrl => CDN.GetGuildSplashUrl(Id, SplashId);
         /// <summary> Indicates whether the client has all the members downloaded to the local guild cache. </summary>