Clear empty selections in GuiView after dispatch

Clear empty selections in GuiView after dispatch

Empty selections can cause confusing behavior for a few reasons:

(1) some functions behave differently depending on whether there is a
selection. If I press delete, nothing happens (where I expect the
character or inset before the cusor to be deleted). If I toggle bold or
emphasize nothing happens (where if there is no selection the entire
word is toggled). There are other LyX functions that depend on whether
there is a selection or not. Further, I wonder if any part of LyX's code
assumes that if there is a selection it is non-empty.

(2) menu options are incorrectly set. For example, the scissors icon.

For remaining empty selection issues, see #9222.

For more information, see:
https://www.mail-archive.com/lyx-devel@lists.lyx.org/msg184758.html