Popover: Prevent hide if already hidden. Fix #1027

[will-shaw]

Prevents unnecessary re-renders of all hidden popovers in the page.

• [x] Make sure you are merging your commits to master branch.
• [x] Add some descriptions and refer relative issues for you PR.
• [x] Rebase your commits to make your pull request meaningful.
• [ ] Make sure that your changes pass npm test, npm run lint and npm run build.

Edit: My changes do not affect the failing tests, however the current master branch is already broken, I can rebase once fixed.

Changes in this pull request Fixes #1027

• Prevents click outside setting state to false if showPopper is already false.