net: report open file and device descriptors ready in select (Cyberpunk 2077 Galaxy RNG seeding)

Co-authored-by: Artyom Zabroda <artyomzabroda@proton.me>

src/kernel/fileSystem.cpp

@@ -410,6 +410,11 @@ std::filesystem::path GetRealFilename(const std::string& mounted_file_name) {
 	return g_mount_points->ResolvePath(mounted_file_name);
 }
 
+bool IsOpenDescriptor(int d) {
+	const auto* file = g_files->GetFile(d);
+	return file != nullptr && file->opened;
+}
+
 // NOLINTNEXTLINE(readability-function-cognitive-complexity)
 int KYTY_SYSV_ABI KernelOpen(const char* path, int flags, uint16_t mode) {
 	PRINT_NAME();

src/kernel/fileSystem.h

@@ -56,6 +56,8 @@ void                  Mount(const std::filesystem::path& folder, const std::stri
 void                  Umount(const std::string& folder_or_point);
 // Returns an empty path when the guest path has no mounted filesystem.
 std::filesystem::path GetRealFilename(const std::string& mounted_file_name);
+// Returns whether d is an open file, directory or device descriptor.
+bool                  IsOpenDescriptor(int d);
 
 int KYTY_SYSV_ABI     KernelOpen(const char* path, int flags, uint16_t mode);
 int KYTY_SYSV_ABI     KernelClose(int d);