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

zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,sol/pygments,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,zmughal/pygments-mirror,sol/pygments,sol/pygments,sol/pygments,sol/pygments,zmughal/pygments-mirror,sol/pygments,sol/pygments,zmughal/pygments-mirror,zmughal/pygments-mirror,zmughal/pygments-mirror,sol/pygments,sol/pygments,zmughal/pygments-mirror