Better error message for duplicate desktop icon (#3446)

* Better error message for duplicate desktop icon

* remove trailing whitespace

frappe/desk/doctype/desktop_icon/desktop_icon.py

@@ -145,6 +145,8 @@ def add_user_icon(_doctype, _report=None, label=None, link=None, type='link', st
 
 			icon_name = new_icon.name
 
+		except frappe.UniqueValidationError as e:
+			frappe.throw(_('Desktop Icon already exists'))
 		except Exception as e:
 			raise e