country: Fix segmentation fault when continent code is not set

Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/country.c

@@ -159,9 +159,11 @@ int loc_country_to_database_v0(struct loc_country* country,
 	}
 
 	// Add continent code
+	if (country->continent_code) {
 		for (unsigned int i = 0; i < 2; i++) {
 			dbobj->continent_code[i] = country->continent_code[i] ? country->continent_code[i] : '\0';
 		}
+	}
 
 	// Save the name string in the string pool
 	off_t name = loc_stringpool_add(pool, country->name ? country->name : "");