Make the `GroffLexer` play nice with being asked to analyse the empty string
Make the `GroffLexer` play nice with being asked to analyse the empty string

aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments,aswinpj/Pygments