Crash when querying tagless nodes

When looking up a node such [6058479131](https://www.openstreetmap.org/node/6058479131), which has only coordinates but no tags, the `osmx query` tool currently crashes:

```
$ curl https://osmx1.protomaps.com/results/b1bbdd89-12e6-4390-b9a2-42a54fc65948.osm.pbf >sample.osm.pbf
$ ./osmx expand sample.osm.pbf sample.osmx
$ ./osmx query sample.osmx node 6058479131
(7.4311092,46.9522392)
MDB_NOTFOUND: No matching key/data pair found, file /Users/sascha/src/OSMExpress/src/storage.cpp, line 74.
Abort trap: 6
```