Avoid killing qemu if passt failed before writing a pidfile.

pid is initialized to 0, so calling pid in this scenario would kill the
entire process group.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Signed-off-by: Peter Foley <pefoley@google.com>
---
 net/passt.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/net/passt.c b/net/passt.c
index 9ed811a514..b3d4b71314 100644
--- a/net/passt.c
+++ b/net/passt.c
@@ -102,7 +102,9 @@ static void net_passt_cleanup(NetClientState *nc)
     }
 #endif
 
-    kill(s->pid, SIGTERM);
+    if (s->pid > 0) {
+        kill(s->pid, SIGTERM);
+    }
     if (g_remove(s->pidfile) != 0) {
         warn_report("Failed to remove passt pidfile %s: %s",
                     s->pidfile, strerror(errno));

-- 
2.53.0.473.g4a7958ca14-goog