[rilmodem] Fix ratmode bad conf file handling

g_key_file_load_from_file loads also dirs, if a bad file/dir was
picked up first then logic deduced wrong the need for ratmode reconfig.

Signed-off-by: Tommi Kenakkala <tommi.kenakkala@oss.tieto.com>
Merge pull request #219 from tkenakka/conffix

[rilmodem] Fix ratmode bad conf file handling