vhost-user: check unix_listen() return value

This check shouldn't be necessary, since &error_fatal is given as
argument and will exit() on failure. However, this change should
silence coverity CID 1401761 & 1401705.

Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20190605145829.7674-3-marcandre.lureau@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

contrib/vhost-user-gpu/main.c

@@ -1160,6 +1160,10 @@ main(int argc, char *argv[])
 
     if (opt_socket_path) {
         int lsock = unix_listen(opt_socket_path, &error_fatal);
+        if (lsock < 0) {
+            g_printerr("Failed to listen on %s.\n", opt_socket_path);
+            exit(EXIT_FAILURE);
+        }
         fd = accept(lsock, NULL, NULL);
         close(lsock);
     } else {

contrib/vhost-user-input/main.c

@@ -367,6 +367,10 @@ main(int argc, char *argv[])
 
     if (opt_socket_path) {
         int lsock = unix_listen(opt_socket_path, &error_fatal);
+        if (lsock < 0) {
+            g_printerr("Failed to listen on %s.\n", opt_socket_path);
+            exit(EXIT_FAILURE);
+        }
         fd = accept(lsock, NULL, NULL);
         close(lsock);
     } else {