Prevent crash on config files with only comments

There was a bug where configuration files containing only comments would
crash `scss-lint`. Change `load_options_hash_from_file` to handle this
case gracefully.

Change-Id: I2e3a02704c84189e94e998b67d2f712abbf861be
Reviewed-on: https://gerrit.causes.com/32734
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane@causes.com>