Weaver does not appear to run in-editor after PR #537

**Describe the bug**

PR #537 breaks custom network messages in the editor



**Repro project**

https://github.com/VirtualBrightPlayz/MirrorNGBug



**To Reproduce**

Steps to reproduce the behavior:

Install `com.unity.nuget.mono-cecil` via git URL

Install `UniTask via git URL.` via git URL.

Install MirrorNG from source.

Send a custom message struct.

An error or two should then be outputted to the console.



**Expected behavior**

Custom network messages send without error.



**Screenshots**

[Image (image): The console shows an error at **[17:55:04]**: **“No writer found for BuggedNetAuth+PasswordMessage. See https://mirrorng.github.io/MirrorNG/Articles/General/Troubleshooting.html”** followed by **UnityEngine.Debug:AssertFormat(Boolean, String, Object[])**. Immediately after, another log at **[17:55:04]** reports a **NullReferenceException: Object reference not set to an instance of an object** in **Mirror.NetworkWriter.Write[T](T value)** at **Assets/Mirror/Runtime/NetworkWriter.cs:183**. Both messages are shown as red error entries in the console.]





**Desktop (please complete the following information):**

* OS: Windows 10 64-bit

* Build target: Standalone

* Unity version: 2020.1.17

* Mirror branch: master/any version after PR #537



**Additional context**

Setting line 51 of MirrorILPostProcessor.cs to `return usesMirror;` instead of `return usesMirror && !usesMirrorEditor;` seems to fix the issue.
