country: Make country codes beginning with X invalid

According to ISO3166, they are only allowed for "private use".
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>

src/country.c

@@ -209,6 +209,10 @@ LOC_EXPORT int loc_country_code_is_valid(const char* cc) {
 			return 0;
 	}
 
+	// The code cannot begin with an X (those are reserved for private use)
+	if (*cc == 'X')
+		return 0;
+
 	// Looks valid
 	return 1;
 }

src/test-country.c

@@ -33,8 +33,8 @@ int main(int argc, char** argv) {
 	int err;
 
 	// Check some valid country codes
-	if (!loc_country_code_is_valid("XX")) {
-		fprintf(stderr, "Valid country code detected as invalid: %s\n", "XX");
+	if (!loc_country_code_is_valid("DE")) {
+		fprintf(stderr, "Valid country code detected as invalid: %s\n", "DE");
 		exit(EXIT_FAILURE);
 	}
 
@@ -101,7 +101,7 @@ int main(int argc, char** argv) {
 		exit(EXIT_FAILURE);
 
 	// Create a country
-	err = loc_writer_add_country(writer, &country, "XX");
+	err = loc_writer_add_country(writer, &country, "DE");
 	if (err) {
 		fprintf(stderr, "Could not create country\n");
 		exit(EXIT_FAILURE);

src/test-network.c

@@ -62,7 +62,7 @@ int main(int argc, char** argv) {
 		exit(EXIT_FAILURE);
 	}
 
-	err = loc_network_set_country_code(network1, "XX");
+	err = loc_network_set_country_code(network1, "DE");
 	if (err) {
 		fprintf(stderr, "Could not set country code\n");
 		exit(EXIT_FAILURE);
@@ -113,7 +113,7 @@ int main(int argc, char** argv) {
 		exit(EXIT_FAILURE);
 	}
 
-	err = loc_network_set_country_code(network2, "XY");
+	err = loc_network_set_country_code(network2, "DE");
 	if (err) {
 		fprintf(stderr, "Could not set country code\n");
 		exit(EXIT_FAILURE);