mention autocomplete does not trigger when there is an active selection

[Kobee1203]

• Enter some text,
• select some text,
• hit @ to replace the currently selected text with an autocomplete : the autocomplete does not trigger

The prevCharIsSpace() function doesn't check if there is a selected text. I added a new condition to check if there is a selected text. I renamed this function to be consistent with what it does.

[StevenDevooght]

Thx, I'll merge this one when I find the time.