add: Fix panic when history command returns nothing

If you disable bash history files alltogether, "history 1" will not contain
anything on first launch of a terminal and therefore the regex
has nothing to parse, so we get an out of bounds array access.
So fix this.

Though it's a dirty silent fail now, I don't want error messages/warnings
everytime I open a shell.

main.go

@@ -140,7 +140,9 @@ func main() {
 		historycmd := args[1]
 		var rgx = regexp.MustCompile("\\s+\\d+\\s+(.*)")
 		rs := rgx.FindStringSubmatch(historycmd)
+		if len(rs) == 2 {
 			add(conn, rs[1])
+		}
 	} else if cmd == "search" {
 		if argslen < 2 {
 			fmt.Fprint(os.Stderr, "Please provide the search query\n")