Fix explicit line break parsing

It's possible for the input to end right after the explicit line break,
i.e. after the second \. This currently leads to an out of range index into
input (as the for loop starts with start+2 and [start:start+1] is the \\).

org/inline.go

@@ -129,7 +129,7 @@ func (d *Document) parseLineBreak(input string, start int) (int, Node) {
 }
 
 func (d *Document) parseExplicitLineBreak(input string, start int) (int, Node) {
-	if start == 0 || input[start-1] == '\n' || start+1 >= len(input) || input[start+1] != '\\' {
+	if start == 0 || input[start-1] == '\n' || start+2 >= len(input) || input[start+1] != '\\' {
 		return 0, nil
 	}
 	for i := start + 2; unicode.IsSpace(rune(input[i])); i++ {