maint: pacify GCC 6 with -Wnull-dereference

src/id.c:249:29: error: potential null pointer dereference \
[-Werror=null-dereference]
       pw_name = xstrdup (pwd->pw_name);
                          ~~~^~~~~~~~~
src/whoami.c:89:11: error: potential null pointer dereference \
[-Werror=null-dereference]
   puts (pw->pw_name);
         ~~^~~~~~~~~

* src/id.c (main): Explicitly exit with EXIT_FAILURE after an eror to
help gcc-6 to detect that the dereferenced pointer is valid.
* src/whoami.c (main): Likewise.

2 files changed, 9 insertions, 3 deletions

diff --git a/src/id.c b/src/id.c
index 218ee5a31..35cbeb564 100644
--- a/src/id.c
+++ b/src/id.c
@@ -245,7 +245,10 @@ main (int argc, char **argv)
             }
         }
       if (pwd == NULL)
-        error (EXIT_FAILURE, 0, _("%s: no such user"), quote (spec));
+        {
+          error (0, 0, _("%s: no such user"), quote (spec));
+          exit (EXIT_FAILURE);
+        }
       pw_name = xstrdup (pwd->pw_name);
       ruid = euid = pwd->pw_uid;
       rgid = egid = pwd->pw_gid;
diff --git a/src/whoami.c b/src/whoami.c
index e58c57528..972cd5539 100644
--- a/src/whoami.c
+++ b/src/whoami.c
@@ -84,8 +84,11 @@ main (int argc, char **argv)
   uid = geteuid ();
   pw = (uid == NO_UID && errno ? NULL : getpwuid (uid));
   if (!pw)
-    error (EXIT_FAILURE, errno, _("cannot find name for user ID %lu"),
-           (unsigned long int) uid);
+    {
+      error (0, errno, _("cannot find name for user ID %lu"),
+             (unsigned long int) uid);
+      exit (EXIT_FAILURE);
+    }
   puts (pw->pw_name);
   return EXIT_SUCCESS;
 }