This patch improves OGL model performance by eliminating unnecessary texture and blend texture file lookups when they are not found. After the first load attempt, a flag in the model data is set if the texture or blend texture file is not found so it is not searched for again.
Performance comparison on a cherry-picked scenario: (among other things, the TNT barrels trigger this inefficiency)
Before
After
Total time in scene rendering function: 2925 microseconds
Total time in scene rendering function: 1168 microseconds
