[PATCH] tail: avoid undefined behavior when polling outputs

[Pádraig Brady]

* src/tail.c (check_output_available): Only check the returned
events from poll() when it indicates there are events to check.
---
 src/tail.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/tail.c b/src/tail.c
index e2e7f4690..938bd3a73 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -369,7 +369,7 @@ check_output_alive (void)
   pfd.events = pfd.revents = 0;
   pfd.events |= POLLRDBAND; /* Needed for illumos, macos.  */
 
-  if (poll (&pfd, 1, 0) >= 0 && (pfd.revents & (POLLERR | POLLHUP)))
+  if (poll (&pfd, 1, 0) > 0 && (pfd.revents & (POLLERR | POLLHUP)))
     die_pipe ();
 #else
   struct timeval delay;
-- 
2.26.2