fix(desktop/chatInput) mentions were misused

formattedPlainTextFilter was not reset when suggestion
box was closed causing the insertMention function to be
called again even thought there was no mention in the
chat input

Closes #3535

ui/app/AppLayouts/Chat/ChatColumn/SuggestionBox.qml

@@ -59,6 +59,7 @@ Rectangle {
 
     function hide() {
         shouldHide = true
+        formattedPlainTextFilter = "";
     }
 
     function selectCurrentItem() {