Fix mesh/texture issues

Part of #841. #### Checklist - [x] I have read the [coding conventions](https://github.com/LostArtefacts/TR-Rando/blob/master/CONTRIBUTING.md#coding-conventions) - [x] I have read the [testing guidelines](https://github.com/LostArtefacts/TR-Rando/blob/master/CONTRIBUTING.md#testing-guidelines) - [x] I have added a changelog entry about what my pull request accomplishes, or it is an internal change #### Description Various mesh/texture fixes for #841.