Fix logic in ldr_ro_manager

Fix argument type for isdigit/isxdigit

stratosphere/ams_mitm/source/set_mitm/setsys_settings_items.cpp

@@ -116,7 +116,7 @@ Result SettingsItemManager::ValidateKey(const char *key) {
 
 static bool IsHexadecimal(const char *str) {
     while (*str) {
-        if (isxdigit(*str)) {
+        if (isxdigit((unsigned char)*str)) {
             str++;
         } else {
             return false;