common/uuid: Add validity checking functions to interface

Given we have a function to invalidate, we should also have ones to
query the validity. Also makes the code more straightforward to read.

src/common/uuid.h

@@ -58,6 +58,13 @@ struct UUID {
         uuid = INVALID_UUID;
     }
 
+    [[nodiscard]] constexpr bool IsInvalid() const {
+        return uuid == INVALID_UUID;
+    }
+    [[nodiscard]] constexpr bool IsValid() const {
+        return !IsInvalid();
+    }
+
     // TODO(ogniK): Properly generate a Nintendo ID
     [[nodiscard]] constexpr u64 GetNintendoID() const {
         return uuid[0];

src/core/hle/service/acc/acc.cpp

@@ -929,8 +929,7 @@ void Module::Interface::TrySelectUserWithoutInteraction(Kernel::HLERequestContex
     }
 
     const auto user_list = profile_manager->GetAllUsers();
-    if (std::all_of(user_list.begin(), user_list.end(),
-                    [](const auto& user) { return user.uuid == Common::INVALID_UUID; })) {
+    if (std::ranges::all_of(user_list, [](const auto& user) { return user.IsInvalid(); })) {
         rb.Push(ResultUnknown); // TODO(ogniK): Find the correct error code
         rb.PushRaw<u128>(Common::INVALID_UUID);
         return;

src/core/hle/service/acc/profile_manager.cpp

@@ -208,9 +208,10 @@ bool ProfileManager::UserExists(UUID uuid) const {
 }
 
 bool ProfileManager::UserExistsIndex(std::size_t index) const {
-    if (index >= MAX_USERS)
+    if (index >= MAX_USERS) {
         return false;
-    return profiles[index].user_uuid.uuid != Common::INVALID_UUID;
+    }
+    return profiles[index].user_uuid.IsValid();
 }
 
 /// Opens a specific user
@@ -304,7 +305,7 @@ bool ProfileManager::RemoveUser(UUID uuid) {
 
 bool ProfileManager::SetProfileBase(UUID uuid, const ProfileBase& profile_new) {
     const auto index = GetUserIndex(uuid);
-    if (!index || profile_new.user_uuid == UUID(Common::INVALID_UUID)) {
+    if (!index || profile_new.user_uuid.IsInvalid()) {
         return false;
     }
 
@@ -346,7 +347,7 @@ void ProfileManager::ParseUserSaveFile() {
     }
 
     for (const auto& user : data.users) {
-        if (user.uuid == UUID(Common::INVALID_UUID)) {
+        if (user.uuid.IsInvalid()) {
             continue;
         }
 

src/core/hle/service/am/applets/applet_profile_select.cpp

@@ -60,7 +60,7 @@ void ProfileSelect::Execute() {
 void ProfileSelect::SelectionComplete(std::optional<Common::UUID> uuid) {
     UserSelectionOutput output{};
 
-    if (uuid.has_value() && uuid->uuid != Common::INVALID_UUID) {
+    if (uuid.has_value() && uuid->IsValid()) {
         output.result = 0;
         output.uuid_selected = uuid->uuid;
     } else {