Fix: Opening files from diff line when not in project root

[sandr01d]

Check list

• [X] I have performed a self-review of my code
• [ ] I have commented my code in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation

Description

When trying to open a file from gd in $EDITOR (alt + e) the wrong file was being opened when the command wasn't executed from the repository's root directory. Fixes #392

Type of change

• [X] Bug fix
• [ ] New feature
• [ ] Refactor
• [ ] Breaking change
• [ ] Documentation change

Test environment

• Shell
• [ ] bash
• [X] zsh
• [ ] fish
• OS
• [X] Linux
  • [ ] Mac OS X
  • [ ] Windows
  • [ ] Others: