guild.by_category() not returning empty categories

[eri]

Summary

I was looking for listing all of the channels (including all types) with categories (sorted correctly like in UI) and found that comment from Danny on issue #2392. I noticed that the result returned by that method ignores empty categories (categories with no channels in it) for some reasons.

Reproduction Steps

• Create a guild with two categories
• Create some test channels under one of the categories, leave the other empty
• Use ctx.guild.by_category() and see results

    @commands.command()
    async def test(self, ctx):
      await ctx.send(ctx.guild.by_category()) # Supposed to return both categories
      await ctx.send(len(ctx.guild.by_category())) # Supposed to return 2

Expected Results

It should return all categories, so 2 in total.

Actual Results

It ignores the empty category and only returns one.

Checklist

• I have searched the open issues for duplicates.
• I have shown the entire traceback, if possible.
• I have removed my token from display, if visible.

System Information

• Python v3.6.9-final
• discord.py v1.3.3-final
• aiohttp v3.6.2
• websockets v8.1
• system info: Linux 4.15.0-99-generic ffmpeg Not played in loop #100-Ubuntu SMP Wed Apr 22 20:32:56 UTC 2
  020

[Rapptz]

This should be fixed by c01bf7c