Fix next discussion jumps to first after resolving a discussion

app/assets/javascripts/notes/stores/getters.js

nextUnresolvedDiscussionId is looking for the current discussion id in one of the unresolvedDiscussionsIds array. Since it the current discussion has been resolved it will return -1 and start over at the beginning.

Suggest searching through all discussions if -1 is returned and dissussionId is provided.

The following discussion from gitlab-ce!30144 should be addressed:

• @pslaughter started a discussion:

  issue: When a discussion is unresolved, it and I use keyboard navigation, it always starts me over at the beginning.

  20190805_keyboard_next_discussion_after_resolve

  I think this has to do with the nextUnresolvedDiscussionId getters requiring that the id passed to it exists in the unresolved array 🤔...

  On one hand, it could be troublesome making these getters work with resolved ID's, so I can understand handling this in a follow up MR. On the other hand, it's a pretty frustrating behavior for users wanting to cycle through discussions, and we may be best to handle it here 🤔...

  What do you think?