linenoise: defensive null pointer check.

* linenoise/linenoise.c (move_cursor_multiline): If the npos
argument happens to be equal to the current position (the
operation is a null move), then no movement is generated. In
that case, no ab_append operation is called, and ab.b will
stay null; this null pointer then gets passed to
lino_os.puts_fn as the string to output, and that will blow
up. This situation hasn't actually been observed.

1 files changed, 2 insertions, 1 deletions

diff --git a/linenoise/linenoise.c b/linenoise/linenoise.c
index cb4b9f41..50e44e00 100644
--- a/linenoise/linenoise.c
+++ b/linenoise/linenoise.c
@@ -1272,7 +1272,8 @@ static void move_cursor_multiline(lino_t *l, int npos)
         ab_append(&ab, seq, wcslen(seq));
     }
 
-    (void) lino_os.puts_fn(l->tty_ofs, ab.b);
+    if (ab.b)
+        (void) lino_os.puts_fn(l->tty_ofs, ab.b);
     ab_free(&ab);
     l->dpos = npos;
     l->oldrow = nrow;