gh pr create -w doesn't open new PR tab when branch had previous PR #320

When using gh pr create to open a new PR with -w, the browser result is an existing PR, previously merged or closed.

Reproduce:

• go to a branch without an open PR and commit some changes.
  • Important caveat: The branch must have closed or merged PR.
• type gh pr create -w
• browser opens old PR: https://github.com/tierninho/PRlist/pull/ccc

Expected result:
Browser open the compare PR page: https://github.com/tierninho/PRlist/compare/ccc?expand=1

When removing the -w flag, the results are inline with expectations as the expected result URL is shown. Alternatively, if a branch had no prior PRs, then the correct URL is opened.

gh version 0.5.4 (2020-02-04), OSX