rlimit: don't assume getrlimit() always succeeds

In times of seccomp it might very well fail, and given that we return
failures from this function anyway, let's also propagate getrlimit()
failures, just to be safe.

src/basic/rlimit-util.c

@@ -42,7 +42,8 @@ int setrlimit_closest(int resource, const struct rlimit *rlim) {
 
         /* So we failed to set the desired setrlimit, then let's try
          * to get as close as we can */
-        assert_se(getrlimit(resource, &highest) == 0);
+        if (getrlimit(resource, &highest) < 0)
+                return -errno;
 
         fixed.rlim_cur = MIN(rlim->rlim_cur, highest.rlim_max);
         fixed.rlim_max = MIN(rlim->rlim_max, highest.rlim_max);