[BUG]: Haven texture leather_red_02 fails to load

The following line does not create a new material and does not load the texture:
```python
bproc.api.loader.load_haven_mat(haven_textures_folder, ["leather_red_02"])
```
The reason is that the no color base texture was downloaded:

When manually downloading the texture from Haven, the issue becomes apparent:

This texture has two color variations, with names `Coll1` and `Coll2`, which are not downloaded by the [download_texture()](https://github.com/DLR-RM/BlenderProc/blob/e04e03f34b66702bbca45d1ac701599b6d764609/blenderproc/scripts/download_haven.py#L58)

Possible solution:
- add `Coll1` and `Coll2` to keys to be downloaded
- check for `_coll1_` in [load_haven_mat() ](https://github.com/DLR-RM/BlenderProc/blob/e04e03f34b66702bbca45d1ac701599b6d764609/blenderproc/python/loader/HavenMaterialLoader.py#L44)as well

Start in blenderproc/scripts/download_haven.py at download_texture() and then inspect blenderproc/python/loader/HavenMaterialLoader.py at load_haven_mat(). Reproduce the leather_red_02 load, trace which texture keys are downloaded and recognized, and verify that the material and both color variation textures load successfully.

Written by the indexing model from the issue text.