Fix: Cycles: NaN Normals from Normal Map

a degenerate triangle could produce a tangent that is antiparallel to
the normal, resulting the mapped normal to be zero, and becomes NaN when
normalized in `object_normal_transform()`. Fixed by falling back to
unperturbed normal in this case.

Fixes an assertion in the attic benchmark scene.

Pull Request: https://projects.blender.org/blender/blender/pulls/140135

intern/cycles/kernel/svm/tex_coord.h

@@ -432,7 +432,7 @@ ccl_device_noinline void svm_node_normal_map(KernelGlobals kg,
     }
   }
 
-  if (is_zero(N)) {
+  if (is_zero(N) || !isfinite_safe(N)) {
     N = sd->N;
   }