Cycles: Fix wrong transparency flag being set to integrator

Patch from be28706 made it so integrator will use last shader's transparent
shadow flag, which is wrong since last shader might not have transparent
shadow while shaders prior to it might have one.

intern/cycles/render/shader.cpp

@@ -386,7 +386,7 @@ void ShaderManager::device_update_common(Device *device,
 		shader_flag[i++] = flag;
 		shader_flag[i++] = shader->pass_id;
 
-		has_transparent_shadow = (flag & SD_HAS_TRANSPARENT_SHADOW) != 0;
+		has_transparent_shadow |= (flag & SD_HAS_TRANSPARENT_SHADOW) != 0;
 	}
 
 	device->tex_alloc("__shader_flag", dscene->shader_flag);