roff: dots are not escaped correctly at beginning of line

[sometimesfood]

While dots at the beginning of a line are escaped correctly, the check in the write method does not catch all cases where there are spaces in front of the dot in a NF:

$ man --warnings test/markdown_syntax.roff > /dev/null
<standard input>:1450: warning: macro `dot' not defined
    (possibly missing space after `do')
$ groff -T ascii test/markdown_syntax.roff 2>/dev/null | grep dot
$

[sometimesfood]

Here's a testcase:

• https://github.com/sometimesfood/ronn/tree/issues/46
• sometimesfood/ronn@30c0d64

[sometimesfood]

Here's a fix:
#48

[thinkerbot]

See #65. That may also fix this issue.

[apjanke]

If you're still interested, I've fixed this case in my Ronn-NG fork at apjanke/ronn-ng#17.