sc_edge fails on single row sf

[mdsumner]

From @mdsumner on December 18, 2017 12:12

sc_edge(nc[1, ])


## causes anglr to fail
anglr(nc[1, ])
 Error in `[[<-.data.frame`(`*tmp*`, "path_", value = c("3f24a604", "3f24a604",  : 
  replacement has 26 rows, data has 0 

Copied from original issue: hypertidy/anglr#58

[mdsumner]

Doesn't fail here

sc_edge(minimal_mesh[1, ])

but it does for this, so is it only when there's a single path?

sc_edge(minimal_mesh[2, ])

[mdsumner]

Fix applied in sc_segment 397f269