Fixes #23: open existing tab if its beside already

[Gregory108]

Fixes eamodio/vscode-find-related#23

Description

Problem described in #23

Checklist

I, @Gregory108 am not an author of the fork I am suggesting to pull into master. Neither am I able at the time to verify the following checklist, as it is written in a language I do not know. Please, allow this violation in order to initiate the progress on the Issue. (And this is the first PR from a fork in my life=)

• [ ] I have followed the guidelines in the Contributing document
• [ ] My changes are based off of the master branch
• [ ] My changes follow the coding style of this project
• [ ] My changes build without any errors or warnings
• [ ] My changes have been formatted and linted
• [ ] My changes include any required corresponding changes to the documentation
• [ ] My changes have been rebased and squashed to the minimal number (typically 1) of relevant commits
• [ ] My changes have a descriptive commit message with a short title, including a Fixes $XXX - or Closes #XXX - prefix to auto-close the issue that your PR addresses

[forivall]

Yeah, my change was quick and dirty, I haven't polished it up for a PR.