Fix inconsistent geometry calculation of partial relations

[1-Byte]

When the API is used with a database which was generated from a extracted OSM file, the bounding box of relations is calculated inconsistently. If the relation contains missing ways, the bounding box is not affected by them. However, if the relation contains a missing node, an artificial Quad_Coord(0u, 0u) gets inserted.

Before: <bounds minlat="-91.0000000" minlon="-214.7483648" maxlat="45.9167004" maxlon="7.8759229"/>
After: <bounds minlat="45.8197974" minlon="7.8613734" maxlat="45.9167004" maxlon="7.8759229"/>