Add a test for #1616

Author: kovidgoyal

Diff for: kitty_tests/mouse.py

@@ -133,6 +133,8 @@ def scroll(x=0, y=0, up=True):
         s.draw('X Y')
         multi_click(x=1.4)
         self.ae(sel(), 'ab')
+        move(2.6)
+        self.ae(sel(), 'ab ')
         move(3.6)
         self.ae(sel(), 'ab cd')
         release(3.6, 1)