Allow getpwuid_r to return missing entry.

If the getpwuid_r method doesn't find an entry with the given ID, it
will still return success (0), but the *result will be set to NULL.
This checks the |result| value so it won't crash if it doesn't find
the entry.

This normally shouldn't ever happen, but it can somehow happen on
iOS simulators.

CONTRIBUTORS

@@ -31,6 +31,7 @@ Fumitoshi Ukai <ukai@google.com>
 Guillaume Dumont <dumont.guillaume@gmail.com>
 Håkan L. S. Younes <hyounes@google.com>
 Ivan Penkov <ivanpe@google.com>
+Jacob Trimble <modmaker@google.com>
 Jim Ray <jimray@google.com>
 Michael Tanner <michael@tannertaxpro.com>
 MiniLight <MiniLightAR@Gmail.com>

src/utilities.cc

@@ -311,7 +311,7 @@ static void MyUserNameInitializer() {
     char buffer[1024] = {'\0'};
     uid_t uid = geteuid();
     int pwuid_res = getpwuid_r(uid, &pwd, buffer, sizeof(buffer), &result);
-    if (pwuid_res == 0) {
+    if (pwuid_res == 0 && result) {
       g_my_user_name = pwd.pw_name;
     } else {
       snprintf(buffer, sizeof(buffer), "uid%d", uid);