input: scroll: call term_mouse_up() once, after all term_mouse_down()

Note that scroll button release events are not actually sent to the
client, but this makes the code more correct, logically.

input.c

@@ -657,6 +657,7 @@ mouse_scroll(struct wayland *wayl, int amount)
     } else {
         for (int i = 0; i < amount; i++)
             term_mouse_down(term, button, wayl->mouse.row, wayl->mouse.col);
+        term_mouse_up(term, button, wayl->mouse.row, wayl->mouse.col);
 
         scrollback(term, amount);
     }