Split on empty sep: fix #552 moar

tests/all.test

@@ -900,6 +900,10 @@ sub("^(?<head>.)"; "Head=\(.head) Tail=")
 ["a,b, c, d, e,f",", a,b, c, d, e,f, "]
 [["a,b","c","d","e,f"],["","a,b","c","d","e,f",""]]
 
+split("")
+"abc"
+["a","b","c"]
+
 ########################
 [.[]|[[sub(", *";":")], [gsub(", *";":")], [scan(", *")]]]
 ["a,b, c, d, e,f",", a,b, c, d, e,f, "]