Prevent monotime overflow

src/lib/time/compat_time.c

@@ -522,6 +522,13 @@ monotime_init_internal(void)
   tor_assert(n <= INT64_MAX);
   tor_assert(d <= INT64_MAX);
 
+  while (d > ONE_MILLION)
+  {
+    n /= 10;
+    d /= 10;
+  }
+  simplify_fraction64(&n, &d);
+
   nsec_per_tick_numer = (int64_t) n;
   nsec_per_tick_denom = (int64_t) d;