testunit: ensure name-options is not nil

Previously if line-number was not present in a call to `ruby-test-test-command`,
the return result would include "nil" at the end of the command; e.g.,

  bundle exec ruby -I'lib:test' /path/to/unit_test.rb nil

This would cause at least Rails tests to explode.
Merge pull request #15 from mjhoy/patch-1

testunit: ensure name-options is not nil