Tighten assertion condition

lib/ngtcp2_rob.c

@@ -160,7 +160,7 @@ static int rob_write_data(ngtcp2_rob *rob, uint64_t offset, const uint8_t *data,
         ngtcp2_rob_data_del(d, rob->mem);
         return rv;
       }
-    } else if (d->range.begin + rob->chunk < offset) {
+    } else if (d->range.begin + rob->chunk <= offset) {
       assert(0);
     }
     n = ngtcp2_min(len, d->range.begin + rob->chunk - offset);