Fix: size_t is not the same everywhere

Author: spnda

src/fastgltf.cpp

@@ -2336,9 +2336,11 @@ void fg::glTF::parseSkins(simdjson::ondemand::array skins) {
                     }
                     // skin.joints.reserve(array.count_elements());
                     for (auto jointValue : array) {
-                        if (jointValue.get_uint64().get(skin.joints.emplace_back()) != SUCCESS) {
+                        uint64_t jointIndex;
+                        if (jointValue.get_uint64().get(jointIndex) != SUCCESS) {
                             SET_ERROR_RETURN(Error::InvalidGltf)
                         }
+                        skin.joints.emplace_back(static_cast<size_t>(jointIndex));
                     }
                     break;
                 }