Fixed some VS warnings

Thanks to Fraggy again !


Former-commit-id: bd0eea66714701b065892d8b69d576e7b3615dd2

src/Nazara/Core/File.cpp

@@ -237,7 +237,7 @@ std::size_t NzFile::Read(void* buffer, std::size_t size)
 
 		m_impl->SetCursorPos(NzFile::AtCurrent, size);
 
-		return m_impl->GetCursorPos()-currentPos;
+		return static_cast<std::size_t>(m_impl->GetCursorPos()-currentPos);
 	}
 }