Allow exit codes other than 0 or 1 if Mypy reports issues

[pwmarcz]

First time contributor checklist

• [x] I have read how to contribute to this project
• [x] I have read the code of conduct to this project

Contributor checklist

• [x] I am targeting the master branch (and not the release branch)
• [x] I am using the provided codeStyleConfig.xml
  • I think so? I opened this project in IntelliJ IDEA
• [x] I have tested my contribution on these versions of PyCharm/IDEA:
  • PyCharm Professional 2022.1.4
• [x] My contribution is fully baked and ready to be merged as is
• [x] I ensure that all the open issues my contribution fixes are mentioned in the commit message of my first commit using the Fixes #1234 syntax

---

Description

As discussed in #103, this makes the plugin not consider exit code other than 0 or 1 to be an abnormal exit, as long as Mypy also reported some issues. Mypy currently returns 2 in case of a syntax error as well as some other errors (such as break outside loop). This change makes sure these issues are correctly reported in Pycharm, instead of treating them as abnormal exit.

Type of Changes

	Type
✓	:bug: Bug fix

Related Issue

Closes #103.

[intgr]

I'm the author of this error handling code and I agree it needs an overhaul.

My thinking has shifted now, I think we should ignore the exit code entirely and instead look at whether stdout or stderr contain any messages. If something is written to stderr, it's almost always a crash of mypy.

In the case of syntax error as you mention, messages are written to stdout.