[hackers] [scroll] Fix some special cases in scrolling || Jochen Sprickerhof

[git]

commit 79dd01d2f78326259f1dbdb3d4d124b94f7bcd8b
Author:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
AuthorDate: Sun Apr 5 22:06:16 2020 +0200
Commit:     Jochen Sprickerhof <g...@jochen.sprickerhof.de>
CommitDate: Sun Apr 5 22:06:16 2020 +0200

    Fix some special cases in scrolling

diff --git a/scroll.c b/scroll.c
index f392fb9..7300231 100644
--- a/scroll.c
+++ b/scroll.c
@@ -283,21 +283,24 @@ scrollup(int n)
                bottom = TAILQ_NEXT(bottom, entries);
                write(STDOUT_FILENO, scrollend->buf, scrollend->size);
        }
+       dprintf(STDOUT_FILENO, "\033[%d;%dH", ws.ws_row, ws.ws_col);
 }
 
 void
 scrolldown(char *buf, size_t size, int n)
 {
+       if (bottom == NULL || bottom == TAILQ_FIRST(&head))
+               return;
        bottom = TAILQ_PREV(bottom, tailhead, entries);
        /* print n lines */
        for (; n > 0 && bottom != NULL && bottom != TAILQ_FIRST(&head); n--) {
                bottom = TAILQ_PREV(bottom, tailhead, entries);
                write(STDOUT_FILENO, bottom->buf, bottom->size);
        }
-       if (bottom == TAILQ_FIRST(&head)) {
+       if (n > 0 && bottom == TAILQ_FIRST(&head)) {
                write(STDOUT_FILENO, "\033[?25h", 6);   /* show cursor */
                write(STDOUT_FILENO, buf, size);
-       } else
+       } else if (bottom != NULL)
                bottom = TAILQ_NEXT(bottom, entries);
 }