[OpenGL] rendering issue in glough's house

[alarixnia]

[misterhat]

i think this is related to models with faces that have less than 3 vertices, noted in https://github.com/2003scape/rsc-models?tab=readme-ov-file#model-bugs

could be something else though, will update if not

[misterhat]

so this model (fourwayplatform-lev 1) does have 7 duplicated faces, but that has nothing to do with this issue. still exists after they're removed:

[misterhat]

it had nothing to do with the model itself (even though it is ugly). the black floor was just perfectly aligned with the base of the model and it was causing z-fighting to occur. fixed by making the back face colour of the floor transparent as well. exact same issue as #76