correct null country error for linkedin

The previous commit invoke $linkedinuser->country->code instead of $linkedinuser->location->country->code, generating a null value if no googleipinfodbkey is configured.
The database column "country" is not null, then the update operation will fail, resulting in inconsistent user info.
Here I correct the source of informations and only set value if is not empty.
Merge pull request #50 from kmiksi/master

correct null country error for linkedin