Initial Condition Checks

On [Line 14](https://github.com/maotcha/markdown-parse/blob/34a4c89fc7bc17165f4c38ad27f829a960e4be64/MarkdownParse.java#L14), the if statement does not check what's inside the parentheses and therefore doesn't check the validity of the link.
Failure-inducing input: `[](.)`