Handle network data with nodes outside the territory

mapMCDA currently fails when a node falls outside the territory.

MRE:

library(mapMCDA)
library(sp)
cmr <- mapMCDA_datasets()

## Correct behaviour, when all nodes are within the territory
risk_layer(
  cmr$mobility,
  boundaries = cmr$cmr_admin3
)
#> class      : RasterLayer 
#> dimensions : 100, 67, 6700  (nrow, ncol, ncell)
#> resolution : 0.1142512, 0.1142512  (x, y)
#> extent     : 8.499454, 16.15429, 1.652267, 13.07739  (xmin, xmax, ymin, ymax)
#> crs        : +proj=longlat +datum=WGS84 +no_defs +ellps=WGS84 +towgs84=0,0,0 
#> source     : memory
#> names      : layer 
#> values     : 0, 100  (min, max)

## Move one node outside of the national territory
cmr_nodes <- attr(cmr$mobility, "geom_node")
cmr_nodes[4] <- cmr_nodes[4] - 1
attr(cmr$mobility, "geom_node") <- cmr_nodes

plot(cmr$cmr_admin3, border = "darkgray")
plot(cmr$mobility, add = TRUE)

## Failure
risk_layer(
  cmr$mobility,
  boundaries = cmr$cmr_admin3
)
#> nerror = 16
#> Error in deldir::tile.list(z): Argument "object" is not of class "deldir".

^{Created on 2020-05-23 by the reprex package (v0.3.0)}

Expected behaviour

mapMCDA should automatically filter (with a warning) the part of the network within borders, and proceed from there.