core: silence gcc warning about unitialized variable

When compiled with -O2, the compiler is not happy about dynamic_user_pop() and
would warn about the output variables not being set. It does have a point:
we were doing a cast from ssize_t to int, and theoretically there could be
wraparound. So let's add an explicit check that the cast to int is fine.

[540/2509] Compiling C object src/core/libsystemd-core-256.so.p/dynamic-user.c.o
../src/core/dynamic-user.c: In function ‘dynamic_user_close.isra’:
../src/core/dynamic-user.c:580:9: warning: ‘uid’ may be used uninitialized [-Wmaybe-uninitialized]
  580 |         unlink_uid_lock(lock_fd, uid, d->name);
      |         ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
../src/core/dynamic-user.c:560:15: note: ‘uid’ was declared here
  560 |         uid_t uid;
      |               ^~~
../src/core/dynamic-user.c: In function ‘dynamic_user_realize’:
../src/core/dynamic-user.c:476:29: warning: ‘new_uid’ may be used uninitialized [-Wmaybe-uninitialized]
  476 |                         num = new_uid;
      |                         ~~~~^~~~~~~~~
../src/core/dynamic-user.c:398:23: note: ‘new_uid’ was declared here
  398 |                 uid_t new_uid;
      |                       ^~~~~~~

0 files changed, 0 insertions, 0 deletions