core: avoid false maybe-uninitialized warning

2026-05-29T18:00:43.7496388Z ../src/core/dynamic-user.c: In function ‘dynamic_user_realize’:
2026-05-29T18:00:43.7497098Z ../src/core/dynamic-user.c:436:29: error: ‘new_uid’ may be used uninitialized [-Werror=maybe-uninitialized]
2026-05-29T18:00:43.7497758Z   436 |                         num = new_uid;
2026-05-29T18:00:43.7498026Z       |                         ~~~~^~~~~~~~~
2026-05-29T18:00:43.7498465Z ../src/core/dynamic-user.c:361:23: note: ‘new_uid’ was declared here
2026-05-29T18:00:43.7498802Z   361 |                 uid_t new_uid;
2026-05-29T18:00:43.7499039Z       |                       ^~~~~~~
2026-05-29T18:00:43.7499315Z In file included from ../src/core/dynamic-user.c:23:
2026-05-29T18:00:43.7499651Z In function ‘dynamic_user_push’,
2026-05-29T18:00:43.7500063Z     inlined from ‘dynamic_user_realize’ at ../src/core/dynamic-user.c:453:13:
2026-05-29T18:00:43.7501021Z ../src/basic/socket-util.h:131:63: error: ‘new_uid_lock_fd’ may be used uninitialized [-Werror=maybe-uninitialized]
2026-05-29T18:00:43.7501897Z   131 | #define send_one_fd_iov(transport_fd, fd, iov, iovlen, flags) send_one_fd_iov_sa(transport_fd, fd, iov, iovlen, NULL, 0, flags)
2026-05-29T18:00:43.7502530Z       |                                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2026-05-29T18:00:43.7503145Z ../src/core/dynamic-user.c:320:16: note: in expansion of macro ‘send_one_fd_iov’
2026-05-29T18:00:43.7503647Z   320 |         return send_one_fd_iov(d->storage_socket[1], lock_fd, &iov, 1, MSG_DONTWAIT);
2026-05-29T18:00:43.7504027Z       |                ^~~~~~~~~~~~~~~
2026-05-29T18:00:43.7504397Z ../src/core/dynamic-user.c: In function ‘dynamic_user_realize’:
2026-05-29T18:00:43.7504888Z ../src/core/dynamic-user.c:360:21: note: ‘new_uid_lock_fd’ was declared here
2026-05-29T18:00:43.7505256Z   360 |                 int new_uid_lock_fd;
2026-05-29T18:00:43.7505511Z       |                     ^~~~~~~~~~~~~~~
2026-05-29T18:00:43.7505882Z ../src/core/dynamic-user.c: In function ‘dynamic_user_current’:
2026-05-29T18:00:43.7506461Z ../src/core/dynamic-user.c:468:15: error: ‘uid’ may be used uninitialized [-Werror=maybe-uninitialized]
2026-05-29T18:00:43.7506895Z   468 |         uid_t uid;
2026-05-29T18:00:43.7507096Z       |               ^~~

2026-05-29T18:26:14.2420944Z In function ‘dynamic_user_push’,
2026-05-29T18:26:14.2421730Z     inlined from ‘dynamic_user_realize’ at ../src/core/dynamic-user.c:453:13:
2026-05-29T18:26:14.2435240Z ../src/basic/socket-util.h:131:63: error: ‘new_uid_lock_fd’ may be used uninitialized [-Werror=maybe-uninitialized]
2026-05-29T18:26:14.2440497Z   131 | #define send_one_fd_iov(transport_fd, fd, iov, iovlen, flags) send_one_fd_iov_sa(transport_fd, fd, iov, iovlen, NULL, 0, flags)
2026-05-29T18:26:14.2442511Z       |                                                               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2026-05-29T18:26:14.2445002Z ../src/core/dynamic-user.c:320:16: note: in expansion of macro ‘send_one_fd_iov’
2026-05-29T18:26:14.2445727Z   320 |         return send_one_fd_iov(d->storage_socket[1], lock_fd, &iov, 1, MSG_DONTWAIT);
2026-05-29T18:26:14.2448345Z       |                ^~~~~~~~~~~~~~~
2026-05-29T18:26:14.2448952Z ../src/core/dynamic-user.c: In function ‘dynamic_user_realize’:
2026-05-29T18:26:14.2451781Z ../src/core/dynamic-user.c:360:21: note: ‘new_uid_lock_fd’ was declared here
2026-05-29T18:26:14.2452287Z   360 |                 int new_uid_lock_fd;
2026-05-29T18:26:14.2454430Z       |                     ^~~~~~~~~~~~~~~
2026-05-29T18:26:14.2454960Z ../src/core/dynamic-user.c: In function ‘dynamic_user_current’:
2026-05-29T18:26:14.2457632Z ../src/core/dynamic-user.c:468:15: error: ‘uid’ may be used uninitialized [-Werror=maybe-uninitialized]
2026-05-29T18:26:14.2458207Z   468 |         uid_t uid;
2026-05-29T18:26:14.2460327Z       |               ^~~

src/core/dynamic-user.c

@@ -357,8 +357,8 @@ static int dynamic_user_realize(
 
         r = dynamic_user_pop(d, &num, &uid_lock_fd);
         if (r < 0) {
-                int new_uid_lock_fd;
-                uid_t new_uid;
+                int new_uid_lock_fd = -EBADF; /* avoid false maybe-uninitialized warning */
+                uid_t new_uid = UID_INVALID; /* avoid false maybe-uninitialized warning */
 
                 if (r != -EAGAIN)
                         return r;
@@ -465,7 +465,7 @@ static int dynamic_user_realize(
 
 int dynamic_user_current(DynamicUser *d, uid_t *ret) {
         _cleanup_close_ int lock_fd = -EBADF;
-        uid_t uid;
+        uid_t uid = UID_INVALID; /* avoid false maybe-uninitialized warning */
         int r;
 
         assert(d);