Emulator

Game Name?
Probably any Wii game (tested only Super Smash Bros Brawl)

Game ID?
RSBE01

MD5 Hash?
Source ISO, untouched: 52ce7160ced2505ad5e397477d0ea4fe
Source ISO converted to nkit.iso: a3957f79521cc9d8bb576f2b33852f8a
nkit.iso compressed to GCZ via Dolphin: 56e8fb25c3f924e2a61ea4130325f700

What's the problem? Describe what went wrong.
If you use Dolphin to compress a Wii ISO in nkit.iso format to GCZ, the resulting file will be a very small (but still valid) GCZ file with just empty partitions.

What steps will reproduce the problem?

1. Use Dolphin to compress a Wii ISO in nkit.iso format to GCZ
2. Check the resulting file:
   Input ISO in nkit.iso format: 6.89 GiB
   Output ISO in GCZ format: 22.4 MiB

Is the issue present in the latest development version?
Yes. Tested on 5.0-11288

Is the issue present in the latest stable version?
Not tested. As far as I know, 5.0 stable doesn't support NKIT processed ISOs

What are your PC specifications?
CPU: Intel Pentium G3258 @ 4.2GHz (OC)
GPU: NVIDIA GeForce GT 440 @ 1GB DDR3
RAM: 16GB @ DDR3-1600 (4x4GB)
OS: Windows 10 (version 1909)

Is there anything else that can help developers narrow down the issue?
Since NKIT can convert plain ISOs to nkit.gcz format directly, I think we can just make Dolphin refuse to compress the ISO to GCZ if it detects the input ISO is in nkit.iso format and call it a day. We just need a fool-proof check in Dolphin to stop users from messing their NKIT procesed ISOs...