Fix Default constructed Material has wrong emissiveFactor #459

[ptc-tgamper]

tiny_gltf.h - properly initialise emissiveFactor;
tests/tester.cc - add test case

[syoyo]

Awesome!

It'd be better to use member initialization instead of initialize members in the constructor. Its more C++11 or later friendly

    std::vector<double> emissiveFactor{{0.0, 0.0, 0.0}};  // length 3. default [0, 0, 0]
    std::string alphaMode{"OPAQUE"};               // default "OPAQUE"
    double alphaCutoff{0.5};             // default 0.5
    bool doubleSided{false};             // default false;

   Material() = default;

There are some ancient code in tinygltf which initialize member variables in the constructor to support C++03 compiler(and gcc-4.8), but tinygltf now drops supporting C++03.

[syoyo]

Awesome! Thanks! Merged!