OverpassTileDecoder: fix unexpected roof:direction (#674)

vtm-extras/src/org/oscim/tiling/source/overpass/OverpassTileDecoder.java

@@ -212,6 +212,9 @@ public class OverpassTileDecoder implements ITileDecoder {
                     case "nnw":
                         tag.value = "337";
                         break;
+                    default:
+                        tag.value = "0";
+                        break;
                 }
             }
         }