fix levenshtein error for #17

Author: hellflame

levenshtein.go

@@ -1,6 +1,9 @@
 package argparse
 
 func decideMatch(target string, candidates []string) []string {
+	if len(candidates) <= 0 {
+		return []string{} // no match at all
+	}
 	ldArray := make([]int, len(candidates))
 	for i, c := range candidates {
 		ldArray[i] = levDistance(target, c)

levenshtein_test.go

@@ -22,6 +22,10 @@ func TestLevDistance(t *testing.T) {
 }
 
 func TestLevDecide(t *testing.T) {
+	if len(decideMatch("xxx", []string{})) != 0 {
+		t.Error("failed to strip empty")
+		return
+	}
 	if decideMatch("linux", []string{"linux", "a", "b"})[0] != "linux" {
 		t.Error("failed to match same word")
 		return