When using :opt:strip_trailing_spaces do not remove empty lines

Fixes #1802

docs/changelog.rst

@@ -49,6 +49,9 @@ To update |kitty|, :doc:`follow the instructions <binary>`.
 
 - ssh kitten: Make argument parsing more like ssh (:iss:`1787`)
 
+- When using :opt:`strip_trailing_spaces` do not remove empty lines
+  (:iss:`1802`)
+
 
 0.14.2 [2019-06-09]
 ---------------------

kitty/window.py

@@ -469,7 +469,7 @@ class Window:
         lines = self.screen.text_for_selection()
         if self.opts.strip_trailing_spaces == 'always' or (
                 self.opts.strip_trailing_spaces == 'smart' and not self.screen.is_rectangle_select()):
-            lines = [l.rstrip() for l in lines]
+            lines = ((l.rstrip() or '\n') for l in lines)
         return ''.join(lines)
 
     def destroy(self):