Link toggle doesn't work as expected

**Describe the bug**
Link toolbar button does not seem to toggle very well. Check the image bellow, it should give you an idea about the problem.

**To Reproduce**
Steps to reproduce the behavior:
1. Select some text to make into a link
2. Click on the link button in the toolbar
3. Now click again to toggle and remove the link
4. Observe that it functions incorrectly

**Expected behavior**
Adding and removing links should be seamless, the same way as you do in most markdown editing environments

**Screenshots**

**Version information**
- OS: macOS
- Browser: Safari, latest
- EasyMDE version: Default, latest

**Additional context**
Great work on this editor, keep it up.

Start by reproducing the link-toolbar behavior in EasyMDE using the listed steps, especially on Safari. Trace the toolbar link action and confirm that selecting linked text, clicking the button, and clicking it again adds and removes the link seamlessly.

Written by the indexing model from the issue text.