Check for nil in argument parsing

[krl]

Ipfs crashes and burns when run as a subprocess. nil-checking solves the problem, even though i don't understand exactly what is happening.

[whyrusleeping]

i'd love to understand why this fixes things before merging

[chriscool]

@krl It looks like it should be fixed by PR #1255 (parse: fix handling of unwanted stdin).
Could you test with #1255 applied?

[ghost]

Yeah it's a duplicate of #1255

[krl]

Ok, closing this, the first crash case was solved by applying #1255
but #1260 still happens.