When g_option_context_parse fails, context and error variables are not getting free'd
which results in memory leaks. Free'ing the same.
And replacing g_error_free with g_clear_error, which checks if the error being passed
is not NULL and sets the variable to NULL on free'ing.
https://bugzilla.gnome.org/show_bug.cgi?id=753854
The variables to store face values are only needed if they will be used to
control the volume. Which isn't the default to avoid potentially being very
loud accidentally. Only create variables when needed.