Fixed edge case issue when cross-compiling to JavaScript for web deployment

[yung-turabian]

I'm learning Lua for a game-jam in place of C++ and I wanted to compile for the web because of the ease of access. This LDtk-loader works like a charm but when using this nifty tool that handles emscripten things (https://schellingb.github.io/LoveWebBuilder/run-project) I got the attached error. I've replaced the load() function with a tonumber() function to simplify the conversion function and now no errors in loading on either desktop or web.