`line_segmentize()` fails to return `n` features reliably

[Robinlovelace]

There are some cases in which line_segmentize() returns an incorrect number of features.

As illustrated below.

failing_line = structure(list(structure(c(324957.69921197, 324957.873557727, 
324959.863123514, 324961.852683597, 324963.822867622, 324969.636546456, 
324976.718443977, 324996.443964294, 673670.123131518, 673680.139281405, 
673686.784106964, 673693.428933452, 673698.960855279, 673709.992098018, 
673722.114520549, 673742.922904206), dim = c(8L, 2L), class = c("XY", 
"LINESTRING", "sfg"))), class = c("sfc_LINESTRING", "sfc"), precision = 0, bbox = structure(c(xmin = 324957.69921197, 
ymin = 673670.123131518, xmax = 324996.443964294, ymax = 673742.922904206
), class = "bbox"), n_empty = 0L)
sf::st_crs(failing_line) = "EPSG:27700"

# Try with rsgeo: 
geo <- rsgeo::as_rsgeo(sf::st_geometry(failing_line))

  # segmentize the line strings
res <- rsgeo::line_segmentize(geo, 4)
res <- sf::st_cast(sf::st_as_sfc(res), "LINESTRING")
res
#> Geometry set for 3 features 
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: 324957.7 ymin: 673670.1 xmax: 324996.4 ymax: 673742.9
#> CRS:           NA
#> LINESTRING (324957.7 673670.1, 324957.9 673680....
#> LINESTRING (324961.1 673690.9, 324961.9 673693....
#> LINESTRING (324969.8 673710.2, 324976.7 673722....
length(res) # should be 4
#> [1] 3
sf::st_length(res)
#> [1] 21.23587 21.23587 42.47173

^{Created on 2023-10-01 with reprex v2.0.2}