The BMesh to Mesh conversion does some checks to the UV helper attributes like selection to avoid copying them to the mesh if they don't contain any meaningful data. However, it does this by looping over all faces for every UV map, not in parallel, so it takes up a large portion of the total time in the conversion. This commit moves that to the existing similar checks. On a 1 million face mesh with 3 UV maps, for me this improved the conversion runtime by 75%, from 174ms to 99ms. Before the serial loops took 88ms out of the total. Combining them with the existing loop over faces only increased its runtime from 29 to 40ms.