util: make it easy to initialize the crtime from the current time in fd_setcrtime()

src/journal/journal-file.c

@@ -2623,7 +2623,7 @@ int journal_file_open(
                  * attributes are not supported we'll just skip this,
                  * and rely solely on mtime/atime/ctime of the file. */
 
-                fd_setcrtime(f->fd, now(CLOCK_REALTIME));
+                fd_setcrtime(f->fd, 0);
 
 #ifdef HAVE_GCRYPT
                 /* Try to load the FSPRG state, and if we can't, then

src/shared/util.c

@@ -7670,6 +7670,9 @@ int fd_setcrtime(int fd, usec_t usec) {
 
         assert(fd >= 0);
 
+        if (usec <= 0)
+                usec = now(CLOCK_REALTIME);
+
         le = htole64((uint64_t) usec);
         if (fsetxattr(fd, "user.crtime_usec", &le, sizeof(le), 0) < 0)
                 return -errno;