gitlab issue gaps with size > 1 not handled correctly

[maks-io]

If there are multiple gitlab issues missing in a row, the current code will not correctly create placeholder issues. I faked a dummy gitlab setup, only containing gitlab issues #15, #16 and #17 (with issues #1 to #14 being non-existent). The current code will turn the set of gitlab issues into
[ { iid: 1 }, { iid: 15 }, { iid: 3 }, { iid: 16 }, { iid: 5 }, { iid: 17 } ]

I tested it with the following code, where the for loop is exactly the same as on the master branch currently:

const gitlabIssues = [
  {iid: 15},
  {iid: 16},
  {iid: 17}
];

for (let i = 0; i < gitlabIssues.length; i++) {
  // GitLab issue internal Id (iid)
  let expectedIdx = i + 1;

  // is there a gap in the GitLab issues?
  // Create placeholder issues so that new GitHub issues will have the same
  // issue number as in GitLab. If a placeholder is used it is because there
  // was a gap in GitLab issues -- likely caused by a deleted GitLab issue.
  if (gitlabIssues[i].iid != expectedIdx) {
    gitlabIssues.splice(i, 0, {
      iid: expectedIdx
    });
    i++;
    console.log('Added placeholder issue for GitLab issue #' + expectedIdx);
    console.log("gitlabIssues now looks like this:", gitlabIssues)
  }
}

When you run this you get:

Added placeholder issue for GitLab issue #1
gitlabIssues now looks like this: [ { iid: 1 }, { iid: 15 }, { iid: 16 }, { iid: 17 } ]
Added placeholder issue for GitLab issue #3
gitlabIssues now looks like this: [ { iid: 1 }, { iid: 15 }, { iid: 3 }, { iid: 16 }, { iid: 17 } ]
Added placeholder issue for GitLab issue #5
gitlabIssues now looks like this: [ { iid: 1 },
  { iid: 15 },
  { iid: 3 },
  { iid: 16 },
  { iid: 5 },
  { iid: 17 } ]