Remove zero width space when you exit open mention

[jasonkeene]

When you exit an open mention via directional keys or mouse click when you move the cursor back into a mention from the right you can notice it takes two presses of the left key to get back in since it's running into the zero width space. Need to remove it when we detect an exit and add it back in when we enter.

[talofo]

This change is also important when you wish to make some word count. If you use the delete key, it will also count that zero width char as 1.